I can choose them all, just not at the same time, by using backups. I plan on saving a copy of the file for that game slot after the parents pass (should be tomorrow sometime) and then choose Fabie to start the new generation. I can later use the backup to choose another of her siblings if I want.

Vida was my first rainbow-hair in the 5 families that I have. 3 of the families are in the 17th generation and are on Pause, 1 family already got the 100 trophies and then I have this family on generation 23.