“if” you could portal/warp between creative worlds for free (and “something” done to make it not abusable in conjunction with survival), then they would need to be steam/psn friends so that “Add Platform/Steam Friends” button in game can make them friends with eachother: warp to friend, add world to your list; you can now warp to your friends creative world from your own creative world for free, or set up a portal between them for free.