If he executed a power of attorney (POA) giving someone authority over his finances, that person can exercise the power.If he did not, you will have to go to court and apply to have yourself (or another sibling or relative) appointed his legal guardian or conservator (either term may be used) during his period of incompetency (e.g. being unresponsive). Without a POA, you need a court order giving someone authority. Ideally, hire a family law attorney or a lawyer who handles elder law (they'd be familiar with the concepts to help you); if you can't afford a lawyer, contact the family court's clerk's office, explain the situation, and ask if they can point you to instructions and possibly sample forms.Note that you can do much without either a POA or court order: for example, if you are willing and able to make some payments out of your own pocket, you can just send them in: so long as at least the minimum payment is made, for example, the credit card company doesn't care whose check pays it. You need the POA or court order mostly to access his bank, etc. accounts.