I have 2 neutered males and a female. The younger male, Khan, is new. I've been trying to introduce him to Sir Issac and Nemesis. The problem I'm having is that although Nemesis has accepted him, Sir Issac remains very territorial and aggressive towards him. I'm scared to leave Khan where Sir Issac can get to him. I admit, I didn't expect this problem because both males are neutered. The real problem is we're leaving in a few weeks and I have to be able to trust my rats to my brother-in-law. He's a great guy and loves my silly vermin, but I don't know if he's up to handling this sort of dominance issue. I need help! Does anyone have any suggestions?