I definitely think you need to broach the subject with your MiL. Maybe by making her aware that YOUR family have to go without to live up to her expectations. I would give some examples eg how much you have "leftover" and perhaps tactfully point out this other couple earn more and have no dependants , if you are not comfortable to talk about it, perhaps your DH could talk to his mum about the unfair financial pressure she is placing on your family?