Some cats are more territorial than others. They show it more when they get to a certain age. The peeing outside the litter box is, most likely, Flash marking his territory. Your friend should try and find some way to state her authority. Let him know that he isn't in charge. Our female cat, Tiga used to attack everyone and everything in our house. We resorted to spraying her with a water bottle whenever she attacked someone or we caught her peeing on something. She knows not to do it now and is a great companion. There's no guarantee that this works with every cat, but it worked for us. Good Luck!
-Alpha Wolf (Shay)