I assume that you are using RTSP for all three streams. In this case, there will be only one stable video stream.
If it is a SIYI camera, you can have two stable streams by running SIYI FPV on both devices, one device using SIYI Camera 1/2, another using RTSP addresses.
And by outputing the video stream through remote controller HDMI port, you can have the third stable stream mirroring MK15 screen.
About the crossbar deviation, I’m afraid this is how it works on ZR10. Do you see crossbar deviation on other zoom gimbal cameras?