I highly recommend https://wefwef.app/ You don’t even have to download it, it looks almost exactly like Apollo. But there’s a bunch of other apps that look like RIF, Sync, etc. to make the browsing more pleasant and usable/familiar.

I believe any accounts joining the family need to first have a Google Payments profile in the country the owner of the plan is in before you can join. Or is that not the case anymore?