Open Family and choose Invite a member to create an invitation code. Share this code. They enter it under Family > Join a family. The code expires in 7 days and can be used once. Members must be at least 13 years old.
In Family, choose Join a family, enter the invite code and confirm. You can choose whether to move your existing items into the family collection; leave that option off to keep them separate.
You share their plan's monthly scans and item space.
Leave family: You keep your own collection. Items you added stay with the family.