I just hit this again and decided to clean it up a bit:
https://github.com/discourse/discourse/commit/75890aed2631ed1858d8d6c756b81d7edb735542
Additionally I fixed some long standing bugs that made that UI painful
https://github.com/discourse/discourse/commit/e143eb595fccf39ddcac3c622eb09249d93aa719
and incredibly annoying
https://github.com/discourse/discourse/commit/eed8ddbb5cd7c9205971b84c2e936605406e95f5
You can now select that a group is a primary group, when this is selected we will set the group as a primary group for all the users in the group.
You can also assign a default title to a group, which means that all members of the group get that title unless it is overridden.