The strange ongoing situation with the Shunryu branch family started when Gojo Minako returned to the Tobiume after a heated disagreement with her in-laws, bringing her two children along with her.

To be more precise: It started when her husband, Gojo Morikazu, decided to follow and stay with his wife and children in the Tobiume, instead of collecting them and bringing his small family back to the Shunryu. Which then somehow snowballed into a good half of the younger Shunryu generation all moving into the Tobiume side of the compound as well.