Mm. The only reasons I can think of would be 1. non-cooperation from the parent; 2. obstructive meddling on the part of the parent's spouse or the POA's sibling.
If it's 1. you will in addition need some way of demonstrating that your parent is mentally incompetent and that his/her welfare depends on your being able to take steps which the POAs are inadequate for.
If it's 2. your application for guardianship may be opposed, and that could get expensive, and could result in the court's appointing an external guardian to circumvent family conflict.
Would you like to say a little more about what's happening?
https://www.agingcare.com/articles/how-to-get-guardianship-of-elderly-parents-140693.htm
If it's 1. you will in addition need some way of demonstrating that your parent is mentally incompetent and that his/her welfare depends on your being able to take steps which the POAs are inadequate for.
If it's 2. your application for guardianship may be opposed, and that could get expensive, and could result in the court's appointing an external guardian to circumvent family conflict.
Would you like to say a little more about what's happening?