I’ve been all over the documentation and search engines trying to find this info, but I must be using the wrong terminology for UE because I keep getting right answers to the wrong question. 
What I am trying to do is to have one CameraActor whose output is the main render that fills the player’s screen, but then overlay one or more additional CameraActor outputs over that, at reduced size. Conceptually, what I need is similar to a mini map or local split-screen multiplayer, but I need to control the relative size of the overlay camera(s) and not just evenly split the screen.
I’m not clear on whether this can be done with Composure or with a CineCamera or with UMG, or whether I need to combine those tools. I’ve seen mention of doing this with Composure and Sequencer, but I need it to happen in realtime during play, not as a cinematic.
It seems I could do what is needed using a render target material on a rectangular mesh, but I’m concerned that may incur a lot of overhead. Is there a better way? Custom code in BP or C++ is doable for me, if there’s no direct way for setting this as camera properties.
I apologize if the Cinematic/Media area is not the right place for this question. Before posting, I scanned this section and a couple of others, and the questions here seem to be most closely related.
This is a fairly easy thing to do in other engines and tools I’ve used, so I imagine it’s easy to do in UE, but I probably just don’t have the right term for a search. If someone could point me in the right direction, I’ll cheerfully RTFM to get the details. Thanks.