Hi Eloo, sorry for the late reply I didn’t see your message before.
To be honest there is a while I did this, sequencer didn’t existe at this time.
As I say the goal is to get 6 vue of your scene as if you are inside a cube, the mettle plugin (again it maybe change during this time) is a cube box in 2d (like UVs) and you have to put each video (front, back, left, right, top, bottom), in the right order.
Inside unreal what I did was created a setup of camera where one is the master and animated (ex the front one) and the 5 other camera are attached like a children to the master one.
Each camera are in square aspect ratio of “1” (not rectangle), and a field of view of 90° (it was for the simple camera not the cineCameraActor, I don’t know how to adapt the field of view to the sensor camera).
Each camera are setup so each one look at each face of this imaginary cube from the exact same center point.
Hope this help more