Meg, if Merlin's not neutered, that could be the reason he's aggressive. Is there a shelter, or Animal Control willing to loan you a trap to catch him and get him snipped? He's gorgeous and sleek like a panther. Does mom's home have a basement that Merlin could be kept in perhaps in a cage? The other possibility is get him snipped etc. and provide food for the new home owners to keep feeding him. Chances are he'll stay there if food's provided, and his aggression will diminish once neutered.