I have legal/medical power of attorney for my dad, can I have my nephews removed from his home?

If they are there with your father's permission, then no, you can't remove them from the home. Do they live there? If they are residents, then the owner of the house or their representative has to go through the correct legal ways to force them to move. This can take some time. Is your father competent? Does he want them removed?

Who has dad's financial POA?

Can't answer the question without a lot more information. Except to say "it depends."

Question 1 - Is your father of sound mind?

There is clearly more to this story.

Are the nephews caring for dad? Are they paying rent? Have you asked them to leave?

Do you have Durable Power of Attorney or simply Medical Power of attorney?

Does Dad want the nephews to leave? Is there financial abuse?