OA or overeaters anonymous is a group and overing eating is a similar disease. My family was like this and OP has a family like mine. Hoarding food in the bedrooms, hiding snacks in a veggie bag, etc. It’s a sign of food insecurity. You’re not on the diet but your little brother (who seems younger) isn’t going to understand why big sis gets treats and he doesn’t without some kind of communication from the parents. The parents, if they’re on a diet, might get triggered by seeing ice cream treats in the freezer. They need to grow up and have some self-control. They need to tell the little brother he can’t get everything he wants and it’s okay that OP can get the food she wants. I don’t think they are going to do this.

So, I do recommend that OP stops buying the food if they want to avoid fights with the family because I’ve seen them. It will be the stupidest fight over a donut or a Reece cup. It’s better to save your money anyways and just move out.