Yes, I think most animations cannot be used out of box. Had the same issue with this huge free mocap database. However I was able to fix some things in Blender and get useful animations.

I will see if animation blending will work good enough once I have a basic set of animations done. Wanted to import everything in Unity, but it seems I'm already years behaind. I get legacy mode
I think I'm supposed to import the .bvhs (maybe with Unity bone naming?) not the blender model together with all animations.

Med however imported my test model with applied animations just the way I expected (meaning it's good, but needs some minor deletion of garbage keyframes I still had left somewhere in the file).