Your male can and just might kill the kittens...He needs to be kept completely clear of them. I know this because it happened to my friends kittens, the male killed all but one of them- horrible

Males want the nursing kittens gone because a nursing mother cannot get pregnant. That means she cannot mate.

To a male cat, that means, get rid of the kittens then she is free game again.

That male needs to be neutered ASAP and so does the mother. she's already had the kittens.

I just noticed the male is neutered already. Neutering does NOT take away the mating drive altogether if it is done too late. That is why it should be done when the pet is young.

However, he still has this drive. Spay her asap, and wean those kittens. that is the best answer i can give.

He was neutered as a little kitten and I do plan to have the mom spayed just as soon as the kittens are weaned. I am not going to hurry that process.

Some cats simply don't like other (new) cats. It may have nothing to do with sexual behavior at all. If that is the case, nothing you can do about it, except keep them separate. Once the kittens are older and more likely to cause retaliation type damage, your troubles may be over. They may just be working out the social hierarchy.