Hm. Just imagine you were young, and scared, and didn't speak the language, and all of a sudden someone dumped you in the middle of the M25 at Rush Hour. Or the middle of Waterloo Station, pre-COVID. With 5 funny-smelling giants (relatively speaking) trying to paw at you, you not knowing if you were going to be hit or not.
We have 2 cats, 1 older rescue, very maternal, and 1 energetic, sweet-tempered young cat, from a family who had a little of 3 beautiful kittens they were looking to rehome. (Older cat had got out by accident from mum's house - mum had the beginnings of dementia and was about to go into a care home.)
Our older cat is very maternal and very loving, and new little cat was brought in as she was pining for her little cat companion we lost way too early in February (vet stated road accident likely; we reckon it was almost certainly some twonk doing 40mph down the side street next to us with cars parked pretty much bumper to bumper down either side, given some of the drivers I see regularly down there thinking they're Senna or Schumacher or someone. I'll refrain from saying what I'd really like to at this point and just say I hope they have lost something of equal value to them in the months between. The cat we lost was very special to me in particular as he was a therapy cat in effect; I was reluctant to get a kitten, being very ill at the time, but he really helped me).
Anyway, my point is that even in our relatively quiet household, with no kids and neighbours round about who are very pet friendly, it took about 2 weeks before the new kitten and our older cat would even stop letting one another know they were on one another's territory. And the first three days they hissed at one another pretty much all the time. Fast forward to September, 2020, and while they fight and have little battles about who's going to get which treats and brushes, they're the best of friends.
There is masses of excellent advice online about how to introduce new pets to your household - cat specific, there's PDSA, Cat Protection League, and many others. I agree that it pretty much does sound as if you might have over committed on this one, so if you haven't already, give the rescue centre a ring first thing tomorrow (later this morning now!) and let them know the true situation.
Did the cat rescue not do a home visit first or insist you send pictures so they could establish if you were a good match for the kits? Pretty much all of our local ones do.