Kittens mate how old ?

the question doesn't make sence i know but complet if i have kittens in my house and they r neutered and spayed would they try to mate i found i calico cat and am rescuing her and her kids but it's more likely she has all females but she didn't let me near her kids yet so i don't know and if i had 4 females in my house that r spayed is there any problem plz help