I recently saw this video which tells the story of a rainbow family in the Netherlands. They aren't polyamorous, it's a gay couple who had a child with a female friend, but the non-biological father raises some of the same concerns about having no legal status with his daughter. They have a written contract that states that whatever they do, the child's wellbeing must come first.

In theory I guess that would eliminate a scenario like the one you described, where the non-biological parent would be asked to leave, but feelings are complicated and there's no telling what would happen if trouble arose.

It's certainly a difficult issue! Thanks for sharing your thoughts.