I have a similar situation with a son who has adhd, picky and with a suppressed appetite due to medication. I also have a daughter who has a very good appetite, and I think would become overweight if she had too many snacks. I stay quite lean, for my sport.
What I do is give my son a very filling supper, when his medication wears off, that my daughter and I don’t eat. It’s usually a hot chocolate, toasted cheese sandwich, fruit and nuts. So he’s getting protein and calories.
For dinner we usually all eat the same thing, but in different amounts. My son will probably just have a lot of carbs and some protein. My daughter will have carbs and meat and some of the vegetables. I have a little of the carbs and a lot of vegetables and protein. If I make something my son won’t touch, I just make him a tuna wrap.
There are some foods I don’t want to eat, like sausages and pizza. If the children are having them, I just say I don’t like them and have something else. I don’t make a big deal and I don’t say it’s about the fat content.
I work full time and I don’t feel this approach is particularly onerous. I don’t think you can blame your own food intake on what people around you are eating.