How to attach irregular model into bones?

I see other small or weird playermodels woking fine, but i cannot port anything well in blender. I mean, when i wanna port model without hands etc. only with pelvis and 2 foots; i can’t setup bones to work with that places. In game it looks like a mess or they don’t want to work at all.

It would be nice if someone show me at least screenshot how the any weird model and bones are set to work fine.

Moved to Workshop Support.