Camera on Camera overlay

Hi, I am pretty new to game programming so this might seem like a trivial question, was looking at sample templates [FPS] to understand and I notice the gun was clipping through the wall and on searching how to solve this, usual solution in other engines is to overlay gun animation over the game play with two cameras, tried doing that, by setting two cameras, camera slot, render groups and fiddling around the GraphicsCompositor, I am getting only one render layer at a time, how do i overlay two identical camera feed rendering different render groups?