Hi, thanks for your question and I'm very sorry to heare about your current situation. My name's Vincent and I'm going to assist you with it.
Could I please first confirm that your question relates to the giving and possible withdrawal (at the appropriate time) of medical treatment.
Thanks very much for that. There is somewhat of a misconception in the UK regarding next of kin and the requirment for his/her/their consent with regard to the giving (or withdrawing) of medical treatment.
In England and Wales, no one (including family members) can consent to the giving or withdrawal of medical treatment in relation to another adult. In situations (like your brother's), where a patient does not have the capacity to give consent himself, the medical professional is obliged to treat the patient in accordance with the best interests of the patient and good medical practice.
Nevertheless, what usually happens is that the doctor who has care of the patient will usually discuss any key decisions (including any information regarding the patient's wishes) with the family prior to action being taken.
Can I help you with anything else? If not, please do take a moment to rate my anwser and best wishes with everything.