My experience is that it depends on the cat. My older tortie (female) took huge exception when we introduced a (male) kitten. In fact, she swiped a chunk out of his ear. Eventually they settled down into a kind of armed neutrality. Previously, our neutered tom was incredibly p*****d off when I introduced 2 kittens, both female. He sulked ever after (at least until he was run over).

Good luck though, they will sort themselves out in time.