Need help retargeting Biped to metahuman with control rig

Ok, here is the situation:

We have an anatomy model with skeleton/muscles as separate layers, rigged in 3ds max to separate biped rigs.

We want to use them together with metahuman in unreal engine, for example for live mocap or hand animation using the metahuman control rig.

I haven´t dealt with Retargeting or any sort of character rig in Unreal so far and I´m a bit lost on how to proceed.

Manuals are a bit sparse on the subject and tutorials are most of the time just about “how do you get this animation from mixamo to work on your unreal mannequin”.

Any tips on some more structured tutorials or wether what we wanna do is actually possible with the combination of 3ds max/unreal?

Its obviously not as easy as importing the rigged max models into Unreal and just replaceing the skeleton with the metahuman skeleton…