Guardianship is a pain in the neck. You will have to keep reporting to the court that awards you guardianship. We have the DPOA, and MPOA, and have stuck with that. We have not had many problems dealing with my FIL's banks, taxes, bills, doctors, etc. It is my understanding that the only reason to go with the Guardianship is if you were not able to get a DPOA in place. Since you also already have the MPOA, I think you already have what you need.
