I asked in the talk page but I don’t think that will get any traction so I just wanted to get a bit of attention here.
This page should describe how to add members. Is it the same as Tag:route=bus#Members?
I don’t know how train route relations are supposed to be mapped - specifically, what members they should have. If you know the answer, please update the wiki page! Or if you’re really not up for it, tell me here and I’ll add it to the wiki.