If you have a POA for a relative, can you file bankruptcy for them - in order to wipe out all of their bad debts?

The court will want them to appear in court, so you can't do it without their approvable, a POA can merely sign for someone if they are not present.

You are not the guardian making their choices for them.

So if they want to file, you can start and work with the attorney, but unless they physcialy can't sign, they should sign the paper work.