My friend has POA over his dad and so does his brother. They disagree about the care for their dad. How do they proceed?

The biggest question here is if the father is competent to make his own choices. If he isn't, then the brothers will have to come to a meeting of the minds based on what their father needs. If they cannot, then a professional needs to intervene to make some decision for them. The main thing is that the father receive the care he needs, whether at home or in a facility.

Having 2 POA's is never a good idea. Hopefully the brothers can come together and make decisions based on what's in the best interest of their father.

This is why is it NOT a good idea to have more than one primary POA. They have to agree to move forward.

Double-check the wording of the POA document to see if this situation is covered.

Is one brother the main POA and the other one the secondary back up? If so, then whoever is the main one proceeds. If they share this equally, then they will have to work this out themselves.