First, I'd get the remaining male fixed, before you bring home a female kitten! That should help eliminate problems, as well as prevent any unexpected litters!

That said, it really depends on the kitten, and if the "boys" see her as a threat, or as a usurper ... I'd follow the time-tested oft-given here advice of keeping the kitten in s separate room for a while, a day or longer, which lets them get used to the smell of each other without being able to attack or confront her. you'll be able to gauge by how much attention - or lack thereof - they give the doorway into where she is how cautious you'll have to be with the introduction.