Wow, that's uh..., yeah. Don't get me wrong, I love cats. More than dogs even. But cats have a kind of aloof personality, that, to me, finding a good home for one of them (I really think the problem has something to do with dominance of one cat over the other) would be much easier than dealing with the hurt when they eventually die.
Even with the cool personality that mine has (he comes over and lays at my feet the minute I start to play my guitar, as well as a few other endearing mannerisms), if he were doing his deeds outside of that box, especially after the investment you made, he'd have to go, not necessarily to a shelter where they'd destroy him if someone didn't adopt him, and I'd just go and get another.
Young cats can be a lot of fun, hint hint. Lol
As an aside, my guy has gotten conditioned to my going into the kitchen when I make myself a sandwich, so I give him a little piece of ham. He was just in there, looking up at me to say, "I'm here. Where's my ham?" I pulled off a piece and dropped it to the floor, but it landed right on his face!
Bastard actually looked at me for a minute, like, WTF dude?