Money help - caring for my grandson on a pension

Hi my grandson is 16 next month his mother is a paranoid schizophrenic and he has been with me 6 years. I am terrified that we might lose his money as he needs to go to lots of clubs and outings and as I’m living on a state pension I couldn’t afford to keep him. I am terrified that he will blow his interview as he can go either very highbrow or go into meltdown. I would need the interview in my home as he likes talking about himself and gets very high faluating ideas of him being a super star and also sounds very plausible.   Help please to manage the forms and how to get our case across.