It's still not clear exactly what you're doing.
Sorry, I'm not sure how else to describe it. You're right though, I am trying to render two scenes to the same back buffer and that is happening but I have to Present after each render _because_ I am rendering to two separate windows, not rendering two views side by side within the same window.
I'm pretty sure my solution is to use another swapchain with its own backbuffer meaning I can do the following:
Render to swapchain 1
Present swapchain 1
Render to swapchain 2
Present swapchain 2
Render to a portion of the backbuffer
Present that portion of it to an hwnd
Render another portion to the same backbuffer
Present that portion of it to the other hwnd
...which clearly isn't working