I am a diabetic in a family that isn't. I have pretty much the same as everyone else, I just leave things out or substitute a few things. So for a roast dinner, I avoid potatoes, maybe have butternut squash instead or load up with more meat and veg. If we have a curry, I have cauliflower instead of rice. If we have lasagne, I have slices of aubergine in my portion instead of the pasta. I think you will get the general idea. Apart from the convenience of not having to prepare two completely different meals, it seems more sociable to be having basically the same thing.