This is the saddest thing I've ever heard of! I know that when an agreement is made it should be stuck to, and if that was the original agreement then I guess sticking to it is the right thing to do. But I, personally, would not want to do it. After all, Tinky and Jupiter are bonded, and even though you could get another kitty in need, so could your sister. And if she was the one to get the new kitty in need, Jupiter nor Tinky would have to be disrupted by introdutions to new situations. Since I do not know the relationship that you have with your siste, I do not know if my suggestion will be possible, but what I'd like to see you do is to try to at least talk to her about how Jupiter would need to adjust to a new home, Tinky would have to adjust to a home without his buddy, You would have to adjust to life without Jupiter and if you wanted to get a new kitty then Tinky would have to adjust all over again. BUT, if SHE got a new kitty, no one would really have to adjust and another cat would find a forever home. This is my suggetstion, after all.....you are just asking her to consider it.