If your male kitty wasn't fixed before sexual maturity...just because he can't reproduce doesn't mean he doesn't not know how to procreate lol.
On a more somber note**
When female cats are in heat they can become extremely aggressive.
My cousin *had* 2 beautiful female cats, a siamese (Belle) and a russian blue (Blue). He's had them since they were babies and bother *were* almost 2 at the time of incident.
I kept telling him he needed to get them both fixed, that I was pretty sure it wasn't a good idea for them to be kept in close quarters while they stayed in heat..which they did..feeding off each other. I think those cats were in heat for 6-8 months solid the last time.
Anyways..One day they went out in the garage (which is not a typical garage..it's set up like a living room) where they were being kept, since my cousin just had a new baby and all, and could only find 1 cat, Blue. They looked and looked for Belle to no avail. They thought someone had let her outside and thought she was lost, they went out looking and calling..no cat.
A week later my other cousin goes out there to watch tv and noticed the room smelt "bad" and started looking around. He found Belle half in the covered litter box and half out. Her eyes were scratched out and she was cut up and bloody. Obviously Blue had hurt her very badly and she was hiding somewhere in the room afraid to come out. She had to go potty and made her way to the litter box...where she died.
I didn't want to make my cousin feel worse then he already did (he liked Belle the most) but I felt that if he had gotten them fixed they wouldn't have been so hormonally charged, because until they went into heat they were very loving to each other..but once they went into heat..it turned into all cats for themselves until the heat cycle was over again (then it went back to lovey dovey).
Moral to long story...get your cats fixed (unless they are show cats).