Thanks for your answer. Yeah I will translate the motion from one armature to another. I know different bonecounts made it more tricky but its fine. I tested it out manuel and it worked.
So I want to write a script where it access the posemode bone 1 add copy rot and copy loc and target/subtarget (to my mcrig) the bones from the source (the imported bvh rig). After adding the first constrainsts it need to target bone 2 of my mcrig and do the same with different target and subtarget.
My main issue is that I dont know how to select another bone in posemode. After trying manuell to click it in Blender it wont show any commandline or phyton line in the Blender info.
I will upload my script to pastebin or something similar and share it here.
The Blender 2.79 didnt help because I try a different way via bone constraints because that work with my target and source rig perfectly.
Still thanks to your help 👍