I have my sister living with me our mum and her dad have expressed they are happy to pay towards her care as it hasn’t worked with them. I’m stuck. I don’t know how much to ask for. On average teens cost their parents between £500 and £600 per month. But that seems like an awful lot to ask for. I’m known for being too nice. I don’t see eye to eye with my mum. I just want to help my sister but the financial help will make a massive difference in our situation.