In any scenario, I will be carrying the most supplies for my family. I am looking for large backpacks or rucksacks to carry the brunt of the supplies for us. I was looking at the following:

http://www.sportsmansguide.com/product/index/used-belgian-military-xl-rucksack-belgium-camo?a=1168746

And wondering if there was anything larger/better for the cost.

I am 6' 1" and 240lbs for reference.

Simple ALICE packs work fine?

If you have to carry it, you might as well be comfortable.  What is your budget?  Have you considered the Mystery Ranch line of packs and their NICE frames?

How many people are in your family?  Any reason why everyone can't wear a pack and help distribute at least some of the load?

large frame  

Just a suggestion

A 2 wheeled cart, with large solid rubber tires will carry far more. So unless you are set on a pack, which you will use for everything else consider that

I did a post on my site about Moms using jogging strollers to carry their gear instead of a pack as well. Most jogger strollers have load limits over 100 lbs. I used to be able to carry 100 lbs over distance, but it wasn't yesterday

That Belgian pack is very similar to an Italian Alpine pack I have.  It is one of the most comfortable packs I have ever owned.  Also you might want to consider the "Hellcat" mod of the alice pack.

http://libertytreeblogs.blogspot.com/2011/04/building-hellcat-hybrid-ruck-from-us.html

Budget is up to $100. 5 people total. Three young kids under 5. They have little mini backpacks with some comfort and snack items, flashlights, clothes, etc. Wife will have a pack, but will probably have to carry the youngest, so she probably has a limit of 20-25lbs for a pack. I will be the main supply mule.

We also have a jogging stroller, one of the BOB strollers. May or may not use it depending on the scenario.

Okay, here's my take on this.

I like external frames for packs meant to carry large loads or be used in non-traditional purposes.  They become scalable.  You can grow or shrink for the size of the load by changing the pack size or adding on/removing compartments (ie, sleep system carriers, rifle scabbards, etc).  You can also remove the pack and lash items directly to the frame using shelves, load slings, pack baskets, etc.  The frames are important for load distribution and stabilization, especially as the weight grows or the load shape becomes awkward.  Internal frame packs force you to have to purchase a new pack as the situation warrants or deal with what you have.  External frame packs make it easier for you to modify your pack to better fit your needs.  

It's no secret I'm a fan of Mystery Ranch because their stuff works and it's comfortable.  It comes at a price though.  If it's outside of your budget, a DEI frame or Alice frame works well too.  Practically anything that fits on a DEI or Alice frame can fit on a MR frame, so if you keep that in mind while shopping for your new pack, you can always upgrade to a MR Nice frame at a later time when the budget allows without having to buy a new pack.  

Surplus packs are a great resource.  I like where your head is on this.  The Alice pack has been the standard for so many decades because it just plain works.  These would be a great start for you and your family.  Read the link to the hellcat pack posted above.  IM me your address and I'll send you two very gently used alice pack bags no charge.  You'll need to purchase Alice frames, molle pads, and molle shoulder straps for these, but they're inexpensive and easy to find.  Follow the instructions for the hellcat mod and you'll be happy with the result.  This will get you started.  Your kids are too small for the Alice packs now, but these will hold you over until you're ready to move into better packs for you and your wife and then the Alice packs can be given to your kids.  

For the money, I like the surplus FILBE packs.  It's a MR-inspired design that shares similarities with a large Alice pack.  It's issued on a DEI frame, but can be mounted on a MR Nice frame at a later time if you choose.  It's a large pack.  It can be purchased in your budget.  Either run it like it's issued from the USMC, or look up the devilcat mod for additional ideas.  Run your Alice pack until you get one of these or something else if you choose.

Your kids are too young to make any reasonable overland movement.  They'll have difficulty navigating obstacles in the hill country over long distances or for long stretches of time.  You can have them walk for a while, but once they tire, they won't have the same motivation to keep going.  You'll also sour them to hiking if you push them too much once they've become tired or lost motivation.  I like the idea of a off-road capable wagon with large wheels and tires.  Something you can use to carry you and your wife's packs while the kids walk, yet once the kids tire, will allow you to pull the kids in while you wear your pack.  The wagon can be used around camp for general utility such as firewood or water collection.  It can also be used in the yard for general hauling of leaves, yard tools, firewood, etc when not "bugging out".  Two kids can sit indian style in a wagon and be pulled relatively easy.  You can also rig a structure around the side that allows you to hang your kids packs on once they stop walking so they aren't cramped in the wagon.  There is nowhere you'll go with 3 kids under 5 that you can't pull a wagon.  Your wife can still push the jogging stroller.  There are mods for jogging strollers that allow you to mount rifles along the side.  Modify the jogging stroller so you can carry your rifles and a kid, yet cover the rifles so they aren't obvious.  This keeps them readily available without looking ominous.  All of your family's packs in a wagon under a tarp, you pulling a wagon, your wife pushing a kid in a jogging stroller, and a couple kids walking looks like just another normal family out for a hike, not a family running away from something.  Over time, your kids will get bigger and then you can work on a load distribution plan between all of you so you don't have to be the family pack mule.  

Thank you for the information. Are all the ALICE frames the same size and it acts like a chassis to add whatever bags/packs you want?

Alice frame is a term for a general design of an external pack frame.  There are a few different metal frame styles on available on the market, but if you purchase an "alice frame", it should have the correct dimensions to work for your application.  

If you can dream it up, you can probably do it with your alice frame.  The pack slides on and off the frame easily.  The hardest part of setting a frame up is to get the belt and shoulder straps installed properly with the correct tension.  It's not hard to do, but it's not something you can accidentally do either.  After it's set up and fitted properly, the belt and shoulder straps don't get messed with.  

You can run the pack by itself, install additional pouches/molle waistpack/modular sleep system carrier and run them with the pack, swap to a different size or style pack altogether, remove the pack and install the load shelf to carry heavy items like ammo cans, lash a $5 trashcan to the frame to be a pack basket for trapping/water collecting/fishing, slide a molle panel on to interface with molle pouches, lash awkward but heavy loads for carrying over distance, install weights for physical conditioning, etc.  The sky's the limit.  

Do some basic Google image searches to see some of the different ways people have used them so you can get some ideas on how you may use yours.  There are tons of resources for ideas on alice pack mods, to include threads on Arfcom, Youtube videos, blogs, and so on.

How many miles and with how much weight are you rucking currently as part of your overall fitness?  That'll tell us how much weight you can reasonably carry to help your family.  

I haven't started to train with a sack yet. The only thing I have been doing remotely related is carrying a 100-lb dumbell around the track at the gym on my shoulder. It is a 1/9 mile track and I can do 1-1 1/2 laps right now.

It's awkward and digs into my shoulder and I have to stabilize it with my arms, so I imagine it would be easier with a backpack.

Get one of these or something similar for your alice frame.

http://store.sorinex.com/Sorinex-Load-Trainer-p/sor-lt.htm

Good idea. A little pricey for what it is, but I have some scrap steel that I can make one with my father-in-law's welder. Thanks.

Pick up and ILBE or FILBE, they are huge, cheap, and reasonably comfy.

That said, no way in hell my family isn't carrying their share, even the kids will be at least carrying 5-10 lbs of something.

What scenario do you picture marching a family of 5 through the wilderness?

Any reason not to just take a vehicle to your destination?

Carrying a lot of weight in a backpack, particularly on rough terrain, takes a LOT of training, experience and is very demanding physically. As well as being at high risk of injury.

If this is not something that you can train up to, and KEEP training for on a regular basis, you need to disabuse yourself of this plan of action and work on alternatives.

What's going to happen to you and your family during this ruck march if you break an ankle or blow out a knee? You aren't a 20 year old Ranger on a march who will get medevaced.

If I was looking for a backpack to do what you want I would not be looking at random military surplus items, I would be looking at Gregory, Osprey, Arcterex, Mystery Ranch, Lowe etc... actual high-quality expedition backpacks. External frame packs suck for anything other than road marching which is why none of the outdoor gear makers pay any attention to them anymore.

If you're actually going to do this, get fitted for a real expedition grade pack at a real outdoor equipment store, and look at packs that have proper frames and suspension systems, and learn how to get it set up correctly with stabilizer straps, shoulder lift tabs, etc to get the weight properly onto your hips and be stable. Alice packs are good as torture devices for youth, not for middle age men to actually carry a load.

Totally agree. 12 miles in rough terrain is a challenge with a 30lb pack. Get a purpose built backpacking pack and skip the tactical stuff. There is a reason you don't see backpackers lugging around 60lb ALICE ruck sacks. They are uncomfortable!

Look at osprey, gregory, deuter, granite gear, etc. in the 65liter size.

It'll take years of training to get to the point where you can carry a heavy load cross-country, day in and day out. 3 kids under 5? You'll be lucky to make 6-8 miles a day, you can't force the kids to walk to the point of exhaustion and who's going to carry them?

Personally, everyone would be carrying only the absolute minimum of survival gear in their small day pack, and I'd modify a gardener's wagon like this to be more effective at cross country travel. Use 1/2" or 5/8" steel rod to make longer axles with angle iron welded to them for bend resistance, so the wheels are outboard of the body, and use saddle clamps/U-bolts or something similar to mount the axles directly to the bottom of the body for a lower center of gravity. Wider tires would be best, and if you use split wheels that'll fit your axles you can bring a patch kit or spare tubes, tools to change them, and a small soccer ball pump. Ditch the handle and make a belt-type harness such as those used with a pulk sled.