Pecking order problems

[rook]

I wonder if I could get some advice please. Until one week ago I had a small Cockatiel family flock consisting of the flock leader (7 years) and father of three now 2 year old youngsters (two cocks, one hen), and a stepmom (age unknown). The natural mother of the chicks died 1 year ago, and now (one week ago) the father passed away unexpectedly as well. After the mother died, things got out of hand and a fight over the single hen (sister and daughter) started, which settled partly with the arrival of stepmom. Now, after big boss died, again, the situation is deteriorating. I have isolated the main troublemaker (??? I think) to avoid serious injuries, but feel very sorry for him too. The two girls are not impressed at all, and none of them is really interested in the boys. The two boys are interested in their sister only, I think...

Sorry, I'll better summarise the chaos, I have got now 4 Cockatiels (three siblings consisting of one girl and two boys) plus one unrelated female, which obviously equals two boys and two girls. Should I now find another female for Mr Troublemaker, or one girl for the boys each, or two boys for the girls, or two boys and two girls, or.... I'm confused now. What is in your experience the best ratio between girls and boys to get them to life in harmony together?

Many thanks, Stephan.