It occurs to me my food expenses would be lower if I didn't need to feed my Mother-in-Law and Uncle. Is there any way I can choose to only feed certain members (i.e. myself, wife and son)?
No, you can't.
Against any desire to let your mother-in-law starve and your uncle suffer from extensive alcohol withdrawal, you can only feed all of them, or none. You can, however, just tick the food every other week, in order to save money.