So you want to know something about this, alright?
I replaced Mudarcher with Slig via NifSkope : I loaded original mud_arc_bv.nif and my custom slig file, copied my Slig NiNode, pasted it in Mudarcher NiNode and removed Mudarcher mesh.

Now about animations :
.kf, xxx_xxx_u.kf and xxx_xxx_l.kf are files with animations, when you open it in nifskope, you'll see many blocks, so I figured out, each character has animation in correct order, so I little bit changed the order, add more anims and this happens.

How did I get other models into MO?
I imported them in Blender, exported as .3ds and imported them to NifSkope.

Hope this helped you.