new kitty problems!

My boyfriend's parents had a female cat that had kittens about 6 or so months ago. About a month ago, we brought home a boy cat who was neutered a week later. About a month after having Giraffe (the boy) we decided to bring his sister home to keep him company b/c he was very attention hungry all the time. We brought her home and the first day she was here, they played very well. Then the female (blacky) ran away for a couple of weeks when she was outside one day. Today she came back home, and I brought her inside. At first the cats played well together, but now I have noticed that the male cat will go up to the female and start licking her but then he will bite her! She doesn't seem to mind someimes, so I didn't think much of it, but once in a while, he will bite and she will hiss at him or whine at him, but he won't stop! There have been a few times where I had to go over and pull him off of her because he won't stop it. I don't understand why he is doing this! I am worried about him hurting her while I am away from home. They are good most of the time, but it is only a few times that he hurts her, or it looks like he's hurting her. If anybody knows why he might be doing this, or what I can do to stop it, please tell me. Oh, also, Sometimes the male cat will be playful with people too and pretend to bite, but he never bites hard at all, just tries to nip at you... but he obviously isn't being playful with our female cat. I figured since he was neutered, he wouldn't be so agressive. Someone tell me what is going on!

Is the female cat spayed?

If she isn't spayed still then he could be reacting to ehr scent changing when she goes into heat. So first off spay her, that should be done immediately after her last litter was rehomed so pregnancy doesn't happen again. Then buy some Feliway and things should get back to normal. I wouldn't worry too much unless there was blood shed. My cats do stuff like that all the time and when the other cat has had enough, they hiss or growl or whine or something. But seriously, spay the female if it hasn't been done. Not just for the kittens but for her health, she will just end up getting cancers and sick from constant reproducing.

No, she's not spayed, we got her home for about a day, and then she ran away so I didn't quite get a chance to do it yet. she has not had any kittens yet, she's only about 6-7 months old. She started fighting back after he kept bothering her though hehe.

Hummmm, she could be starting in heat and the male is interested. I would suggest that perhaps you get her spayed as soon as possible.