I thought we were talking about volumes, not brushes.
But why would you use BSP, that is meant to be used for blocking, in a blueprint?
If you need a trigger volume with an exotic shape, compose it of simpler shapes instead.
A BP within a BP is always a child.
Network replication was not part of your initial post.
I never said that I do replication.
Maybe not a complete house, but I can make a little example of what I mean 
… And while doing that, I may have discovered a bug/limitation.
But before complaining about a bug, I want to double check on Answer Hub first.
Because I remember in the past I could setup/control child actor components via interface messages.
but for some reason that does not seem to work now…
Ill make a clean repro and update the Answer Hub link here.
Maybe Im just missing something (has been a while since I fiddled with interfaces).