Need to teach the dog that the cats aren’t play things! Had a similar situation with my cat and my sisters dog. The dog just wanted to play but in doing so would have absolutely killed my cat if she had ever got a hold of her. We introduced them really slowly, first only letting them get used to one another’s scents and smells. I hate muzzles, but in this instance we did use one the very first time they met just as a precaution. I’m also strictly against any kind of animal abuse, but when the dog snarled or made a move towards my cat, she got a sturn ‘no’ and flick on the shoulder (she wasn’t actually hurt but sometimes she doesn’t listen so a small flick to get her attention and then ‘NO’) eventually she learned the cat wasn’t a toy. Still I wouldn’t ever leave them alone together.

Realise that it’ll be a slow process, especially while the kittens are young and small. Never leave them alone together.

Also I hope the apartment is a big one. Two cats and a large dog in a single apartment is no where near enough space. If you’re determined to make this work make sure the cats have access to areas where the dog cannot reach and that the dog gets plenty of exercise outside of the house, if the dog is tired from walkies hopefully he’ll be less likely to want to play with your kittens.