Wel you can try to retarget the animations exported from UE4 in , for retarget the animations (mostly mocap data in bvh) I use MakeWalk (included on ’ tools’ from makehuman).
Also i think you can try the tools that come with , since the bones are the same (the deform bones) if you use the UE4 animations, just turn off Ik for the rig, constraints etc… to avoid any interference.
I hope that helps
Greetings!