I have been reading about how you rescued Orangekitty and how worried you were whether to keep him or not and was very glad to see your happy kitten pics.
I admire you for taking responsability and you have taken it when you rescued him.
However there can be a limit for what a person can take -just in general. And I think it is ok to say no at a certain point. Everybody must decide where this point is for him or her.
And if you have to choose you are not forced to choose the thing that is the most uncomfortable to you.
Would you ask yourself also if you had Orangekitty for a year or so?
Is there a possibility that you find another solution for your aunt's cat?