You cant have the nice little scroll showing who holds what position, but you can do it through traits. EB uses a system like this; They made a single roman faction (SPQR). All of your characters can progress through the ranks, gaining benifits as they do. For your "twin king" case, you cant have 2 faction leaders, but it is very possible for them to have the same trait "King" or something, with say +5 influence or soemthing.

Check out EB, v1.1 just came out so your in luck. It shows perfectly how to do it. But, it is VERY adictive ( ), so you may forget about your mini mod. In that case, just ask one of the EB team members, they can explain it short and simple.

3rd paragraph, but if you don't want to ask around, the basics needed to make "offices" and such are simple traits and triggers. The triggers can be anything you choose. If you want a two king system, for example, make it so to be elected King you need to be 30 or something.

Have fun and good luck