Hi Dirk,

Delta Cam Transf is primarily for PTZ cameras when there is no position data available from the camera. You can set the position of the camera with it. The exact position of the camera is the camera's image sensor's position.

Delta Head Transf describes the difference between the position of the tracker and the position of the camera's image sensor center. It tells how to modify (move and rotate) the placement reported by the tracker to get the actual camera position.
Usually, the trackers are placed a few centimeters from the Camera's image sensor. You will have to give that few centimeters for Delta Head Transf, including any rotation of the tracker compared to the camera.
Note, most professional camera tracking systems will already have this calculated and so, you won't need to change the Delta Head Transf in these cases.

Delta Head TransfB and Delta Head TransfC come into play when using the BillboardB and BillboardC. The reason for these billboards is that the camera could show multiple people at once and you want to separate them into different billboards. More on that:
https://aximmetry.com/learn/tutorials/for-studio-operators/setting-up-virtual-sets-with-tracked-cameras/#compositing-modes

So in your case, you will have to set the Delta Cam Transf for the 2 fixed cameras without any tracking. For example, set them up in Input 1 and Input 2 and in Origin 1's Delta Cam Transf and in Origin 2's Delta Cam Transf.
Most likely, you won't have to touch anything in the Origin for the mo-sys tracked camera. However, when setting up the PTZ Cameras, the Delta Cam Transf will have to be measured from the mo-sys tracking's zero point (0,0,0).