Shellfish, invertebrates (crab, lobster), serving meat with dairy products all aren't kosher. Ergo no cheese on sandwiches, lasagna, most pizzas etc
Most Jewish schools keep kosher kitchens. shrimp gumbo was a big no-no.
Depends on how observant they are. Keeping kosher isn't too hard once you get started. Some families keep two sets of cookware and dishes.
Ma Danby has a rather eclectic family. She's half-Serbian/Montenegrin and half Irish/Penna Dutch. Her older brother married a Jewish girl from Indianapolis. Her sister a Jewish guy from Manhattan, family is one of the diamond industry families. Hey younger brother a girl who is half Black and half Japanese, with deep ties to the music and acting industries. All have Jewish friends. Going to Hannukah dinners used to be a hoot, listening to all the stories of grandmothers and great-aunts, and comparisons of brisket recipes, latkes recipes, what is the right way to grind the onions, What Onions?, secrets for matzoh balls. And then a few days later at her parents for St. Pizza Day when all the kids select and decorate the tree, and then Christmas Eve with the Serbian extended family at Ma's parents.
Then we go over to our kosher friends for New Year's Eve, and get to hear their best ways for brisket and latkes.
I hate to admit it, I never met a brisket or latke I didn't like.