I didn't include models because the models used are not mine. Are you sure you can't retarget the animation to another model in Unreal? I can't really test it in Unreal as I don't use it, but from what I've seen and heard online you can retarget an FBX animation Rig to another model in Unreal using a T-pose.
I found this online let me know if this helps or if you need anything else: https://docs.unrealengine.com/4.27/en-US/AnimatingObjects/SkeletalMeshAnimation/...