Oh, this is awful... I can see both sides of the story and agree with them both >_< I think your sister should be able to get back her cat (it's obvious that she missed him a lot, and something like that would be hard to get over) and I think that you should get to keep him, since both you and Tinky obviously love him a lot... Since I'm that split myself I honestly can't give you any useful advice. I hope for the best for all of you, including that little kitten.