Before I start meddling to no avail (I'm still pretty inexperienced in M&B modding), would it even be POSSIBLE to create split kingdoms? Something like: Kingdom X is ruled by the faction Clan A, where Clan B, and C, are also constituents of X. Members of B and C act identically to members of A when it comes to things like defense of territory, feasts, orders from the marshal, etc. The territory of Kingdom X would be made up of the holding of all three Clans and labeled as such. However, Clans B and C also retain the possibility of deserting as a group, kind of like individual Lords can. In an ideal world, B and C would have the ability to desert as a group to another kingdom, or begin operating independently as their own kingdom when they desert, bringing the territory they owned with them.
It's pretty far-fetched sounding in my opinion, and sounds incredibly vulnerable to extreme bugginess; But if such a thing is possible using the module system, I'd like to see what I can try with it, even if just a fraction of what I'm asking for could work. If it's worth anything, the mod I'm building is using Floris as its base.