Add one more column in realms view, showing the endpoints which are using the realm. There should be a limit of text length showing ... at the end if list is too long.
Add read only field to realm's edit view with full list of endpoints using the realm.
make realm name clickable, click on name should trigger the same action as edit.
Update: if this is not very hard (and I don't think it is) instead of truncating the text which is not fitting the column, it can be wrapped to next line. All cells in the "grid" should be then aligned to top of the line.