At the moment you can only leave a family if you are its only member. This usually happens when you set up your own family before discovering your partner had already made one, and you want to join theirs instead.
When you leave, the family you set up stays behind. No one can see it, not even you, and nothing from it comes with you. It is kept, unreachable to everyone, for 90 days in case something went wrong and you need our help putting it back. After that it is deleted.
If joining the new family does not work for any reason, nothing changes: you stay in your current family exactly as it was.
If you need help, contact us through symplano.com/support.