I only really know of Arendelle and the Enchanted Forest in the same realm. I suppose Neverland might be there, but it's hard to find. Or it might be its own realm entirely. Only the Hatter can go to all the realms, beans are needed for the others. So, we definitely don't have a united anything.
Yeah, I gave up on tracking my family tree since there's so many weird connections in it. Technically, through my son I'm also related to 'Beast' and 'Belle', since his grandfather is what I think is supposed to be our Beast.