Mating Behavior

Hello everyone. I have 2 pairs of budgies. Both pairs have mated. First pair has three children and the other pair has one. Unfortunately male budgie of the first pair has died. Now three children are all grown up. the mother was very curious to go to the other cage where other pair is kept.

So I made both cages to be together. Suddenly that female budgie started mating with the male budgie of 2nd pair.

Both female budgies were fighting then. What should I do now?

I have separated them now but I don't want female budgie who mated with the male of other pair to be separate.