We're Mexican and it isn't uncommon in our culture to live with our parents until marriage or we move out with an SO. My sister has a boyfriend but he's even fatter and also lives at home.  I've told my parents many times she steals food but they say "food is meant to be eaten" or "all food in this house is for everyone to share". My mom doesn't want to get involved and she shouldn't have to. We're fucking adults but my sister still acts like a damn child.