My male cat suddenly hates his sister after two new kittens arrive?

The kittens need to be kept in the bathroom for a minimum of 2 to 4 weeks. This gives Domino and Sierra time to adjust.

Without this, you've essentially brought 2 new "roomers" into the house without their "permission". Would you do that to your kids?

Cats find this very stressful and upsetting.

Cats are also territorial, and Domino probably smells the kittens everywhere, and can't tell where the scent is coming from. Even Sierra may smell a little like the kittens, so he is very confused.

You NEED to confine them for a bit. Bring them out for brief play periods, whiled Domino and Sierra are put in a different room.

But, 2 kittens? Domino may feel you've crossed the boundaries by doubling your cat population. One more might work (preferably the female), and may bond better with the adult pair. Two is a lot for the adult cats to take.

All of them will need to be spayed or neutered, or you will continue to have fights.

You have too many cats, rehome the kittens and make sure all your cats are neutered or spayed.

I'd say he's feeling stressed by the kittens and is taking it out on whoever's handy. This isn't unusual in multi-cat situations.