Flirting budgies

[Amandastander]

Hi my 2 females and 1 male budgie is flirting terribly with my sister in laws male and female, and we can definitely see who's likely to pair up should they be together. What worries me is that they may harm each other if we pair them off, seeing that hers are the english show budgie and they are bigger than mine, how do we go about it and should we go about it? I have a nice big cage that would be perfect for breeding, and its almost spring here in south africa, the one female is a bit out of season and she doesn't take part in the flirting but the other one tries to get her hind and vent into the other cage through the bars! Help asap