Kittens and their parent cats

Question
Hi, Karen -
Thanks so much for your fast response.  Your answer sounds right.  It makes sense now. One more thing to ask though...The male cat has been neutered since getting his sister pregnant. So I don't think he feels threatened by another cat or the kittens are interfering their parents' mating situation.  Do you think, perhaps, since the kittens play too rough with the mom sometimes and they actually hurt her, the male cat tackles the kittens (not too hard though) trying to protect her?  It looks like that sometimes...like he's asking her, "Are you okay?" right after he tackles the kittens and softly grabs them.
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-----Question-----
I have two cats, brother (neutered) and sister (not spayed.) Before the male cat got neutered, the female cat had gotten pregnant by her brother and had two kittens a month ago.  They seemed to get along fine until recently when the kittens started coming out to play.  It looks as if the parent cats are playing too rough with their children.  I'm worried that they might hurt the kittens by accident.  I know that the mom cat disciplines the kittens when they play too rough to teach them how to play properly, but I hear that the father may harm the kittens, although chances are less likely since he is their father.  Should I keep the father cat separately from his kittens?  The kittens never screams when the father plays with them even though it looks like he's hurting them sometimes.  The kittens however, screams when the mom bites them on their neck when they play too rough.
-----Answer-----
Hi Midori,

Congratulations on your new additions. There are a few reasons the male is rough housing with the kittens. One is that he is asserting his dominance over the kittens.
Another reason is that the kittens are annoying him.  
Also male cats will attack a female's kittens because she has gone into heat again. The male feels the kittens are interfering with him mating with the female.
From what you are saying it sounds like the male is just either annoyed or asserting dominance. I wouldn't remove the kittens. Just try to keep an eye on them. They will be old enough to take care of themselves soon. Good luck with them.

Ciao, Karen

Answer
Hi Midori,

That could quite possibly be what's happening. You have to remember one thing though. Even thought your male was neutered after getting your female pregnant, he still has a lot of the male hormones in his body. So even though he can't get your female pregnant he still can react to her going into heat. And he will protect her still as a potential mate. But it sounds like he is just doing his parenting duties towards the kittens. And again, as the kittens get older they will turn their attention from their mom to themselves.  They will start playing amongst themselves. And this is the fun part of having kittens; watching their antics. If you have anymore questions please don't hesitate to write back.

Ciao, Karen