When I was doing my genealogy work sometime ago, I discovered that few of my ancestors were living in polygamy. I learned that, as a rule of thumb, the second wife usually either the first wife’s sister or her closest female friend. It had nothing to do with “rank” but friendship. The relationship between employer and employee often created strong friendship bond over the time which may be why those “wife”in old language as mentioned above choose their “handmaid, maid, nurse, or servant”, or whatever a subordinate called. It may be a decision that had nothing to with “rank” but a really closed friendship that willing to share a husband with.

Of course, I may be wrong about this, but this is what I’m currently thinking of.