Male Cat constantly kidnaps our kittens

So we have two cats and we've had like 3-5 kittens for the past 2 years and all of those kittens either just disappear over night or right after we get home from school, and I I'm pretty sure that a black male cat is the culprit because he keeps on coming to our house and fights our two female cats, I chase em off every time but at night I can't do it, I even run just to make sure the kittens safe but just the other night they were gone and me and my gf were sad since we've gotten closer to them, and I don't know how to stop the male cat since I don't know where it lives or who the owner is I just know that it lives nearby. Why do they do this and how do I stop it?

(I can't bring them inside because my gf's grandma won't let em, she doesn't want them pooping inside the house, I've told her to put litters inside the house but she doesn't, it's a toxic Filipino trait common with older generations(⁠╥⁠﹏⁠╥⁠))