Using a skeleton from a lowpoly for a highpoly model (Mixamo)

Since I’m still pretty recent at the whole unreal game, I’ll just say what I’m trying to accomplish and you guys can point out where I’m failing.

I have a few sculpts in zbrush which I want to rig with Mixamo and export to Unreal. The models are pretty dense, so I’m trying to figure out a way to actually upload them to the site to rig. I assumed I could just use the lowest subdivision for the rig and use it for the higher one. Now I might be just doing something stupid here and not realising it.

I import the fbx from Mixamo to UE4, then try to import obj/fbx file for the high density model. The model is the same, just got more of 'em polys. I constantly keep getting the ‘Failed to merge bones’ error and whichever way I go about it, it just breaks down.
I’ve seen that some people have gotten this because they had multiple different objects in the fbx file?
I just need my detailed bois to be nice and posed in Unreal somehow.

Is there any way for me to fix this, or use LODs(which break too) to get the high poly models posed?

I’m still quite green at this, and no matter how many tutorials I watch I still find new ways to confuse myself. Any help would be great. Thanks in advance :slight_smile: