Few questions. First is my 7 year old daughter is finally ridding without training wheels. I've heard that a bike designed for kids but mimics an adult bike would be much more enjoyable etc for her instead of the $80 Walmart bike. Is it worth spending 2-300?
  Bonus is with and I will try and ride more with the kiddo so hopefully get back into shape a little. Wife has a crappy Walmart mountain bike that's 12 years old. Obviously I'd like to get her a new one. Thinking specialized jynx.
   And lastly my bike is a 13 year old giant rincon that has less than 50 miles on it.  But the front shocks are bad and tires are dry rotted.
  Is it worth it to invest in fixing up my bike or should I just buy a new specialized that I recently looked at?
  Other name brands besides trek,specialized, giant? Those are the local brands anyway.  
  I think dicks sporting goods sells GT and maybe diamond back? But I'm not sure of those brands.
   Ridding will be primarily gravel,dirt, grass with little pavement.  
  Oh and I'm 6'3" 270lbs. Not sure if I need a better quality bike because of my weight?

Thanks for your time

I've just gotten into MTB, and got a 2018 Cannondale Trail 3, but I got it with the intent to ride trails which so far is what i've done.  True MTB's aren't as pleasant to ride on pavement and you may want some sort of hybrid.  I'd try a local bike shop, they can typically help you out a ton and a good one will get you exactly what you need.

I got my 7 year old one of the Dick's store brand mountain bike's and it is fairly well features, but for $159 it doesn't have the components that something higher end would have, but i don't want to spend a bunch when they keep growing out of things.

Tires are cheap and easy to change.  I don't know much about shock maintenance as I was mainly a road biker.  Bonus - you can tailor your tires for your planned riding conditions:  slicks for pavement, knobbies for mud, or something in between for dirt roads.

As far as putting money into a kids bike - any others coming behind your daughter who could also use the bike?

Regarding good deals, some of the best bang for the buck deals out there are Fuji bikes "Performance Exclusives" which are special runs of bicycles that Fuji produces for Performance Bicycles.  I have a Cervelo road and triathlon bike, but my cyclocross and mountain bikes are Fuji.

I'd suggest you find a local bike shop you would be comfortable with. Let them help you out. They will likely be able to help you find bikes within your budget and they will fit and function better than something you buy in a big box retail store.