Steakhouse 71 for lunch or dinner, Kona Cafe for breakfast. I think everyone can be happy with the food choices at both of these and they aren't overly crowded seating.
Cali Grill, Citrico's, Ohana's - also solid choices based on monorail access are the fact you are staying at Poly.
If you think they will go to a park with you:
At EP - Garden Grill for a character meal because it is family-style and they won't have to get up for a buffet. And, if they give up after the front of the park, you aren't deep in World Showcase.
At AK - Tiffins is fabulous - though a bit adenturous (Well, the burger and short-rib are pretty meat n potatoes.
At HS - Mama Melrose or Brown Derby (I don't think Sci FI or Prime Time will work well for you.) If they like bbq, Woody's is another great family style.
At MK - LTT.