No assets - is there an alternative to a power of attorney or deputy?

Silvertabby

Apologies if this sounds brutal, but if your dad's time is likely to be short then don't waste it by fretting about his finances.
When the time comes, any money in his bank account may be used to help pay for his funeral expenses (unless he owes the bank money, in which case they will recover their own debt first).

You and your brother can arrange for the funeral as you wish.  However, it's vital that you don't involve yourselves in any of your dad's debts - including overdue rent - as this could cause no end of problems for you
  
You will just need to send photocopies of his death certificate to his creditors, stating that the estate is insolvent, and that no-one is dealing with it.

My sympathies to you all at this awful time.