Mom’s bad cat behavior, Who is at fault?

My Mom got a cat for christmas . It has been starting doing a bad cat behavior in the house. I have kept the litter box clean and it still has cheap Acomplia been bad and I’ve decided to get rid of it. Who is more at fault for the cat’s behavior?
It was my stepdad who picked the cat up from the place we found the cat at as well.
and we live in the same house and it kept ****** in mom’s bed.