I am still having issues trying to get Adam to work with the Epic Skeleton.
When you originally imported Adam and his animations, rather than creating a new skeleton, could you select the existing Epic UE Mannequin Skeleton?
This way, all of your assets will use the epic Mannequin Skeleton.
The problem I am having is that retargeting or even exporting and reimporting the animations onto the mannequin result in a poor animation. I think the base pose may have been off - did you use a T-Pose or A-Pose for the base pose of Adam? (I think the UE Skeleton uses A-Pose)
It is going to be a lot of work to try and get it to work - if you could get it to work on the Epic Skeleton, then all purchasers of Adam could benefit…