After examining some other figures for the Victoria 3 base, I've determined that one of the things being done to get the hip to follow the thigh is typically to set the parent of the thigh to the hip in the Setup room. By doing that myself, I'm able to get the hip to follow the thigh, but the problem is that the entire hip follows the thigh rather than just the buttock or thigh.

For example, when I mimic the method of adding all of the polygons of the skirt to the Hip group and then parent both the left and right thighs to that Hip group, moving just one of the thighs causes the entire hip to move with it.

I looked into the Joint Controlled Morphs (JCMs) recommended in the posts above, and they don't seem to fit what I'm trying to do.

I'd like to think I'm halfway to figuring out how this is done, but it's quite confusing.