I doubt that adverse possession applies to friends who will not leave, especially since the son once gave permission for the friend to use a room. I never heard of adverse possession being asserted about one room in a house.This guy may have squatter rights now. this person is no friend hes taking advantage of everyone. he needs to go. were I live squatters seem to have lots of rights and getting rid of them is not easy. google says: There are no “squatters rights” in Tennessee, but there is adverse possession. again check the laws in your area, maybe even speak to the sheriff.