After you verify they are working feel free to unsubscribe of course.
Edit: after reading it again I’m a bit confused to what your problem is, so here is a quick run down of jow things should work.
From your own account, use the search bar to search for a community in another instance, there try to see button for about community (it might be different on each app) and lastly press subscribe. From yhere, all your subscriptions should appear the same regardless of where they come from.