'if someone other than the next of kin agrees to treatment on the patients behalf the hospital could find themselves in trouble if things go wrong. '

Actually Jane no person can give, or refuse, consent on behalf of another adult...in UK law if a patient is unable to consent to treatment the decision to treat...or how to treat... has to be made by a medical practitioner, if something goes wrong a court would only need to be satisfied that the practioner acted in what was reasonably thought to be 'in the patient's best interest' However who is next of kin is more important if someone dies... the body of the deceased effectivly becomes their 'property'... and they have the responsibility to dispose of it in a proper manner... that can be quite costly... both financially if the deceased has no estate... also emotionally for a young person... time for you & the rest of this chap's extended family to get their heads together I'd think.