Just find a way to peacefully coexist without getting all up in one another's shit.
I'd sooner have more PCed characters and a legacy character that inexplicably doesn't interact with his or her parent character than fewer PCed characters. If it means reworking the backstory, rework the backstory. If it means the legacy character has to go on a shit lot of solo missions and develop a rogue's gallery of their own, do that.
Heck, it's better than playing a legacy character that's joined at the hip to their parent character and are reliant on them for material.