offering

During the Mid-late game i see many new clans spawn on the world, some declare war on you, I notice overtime factions will recruit these clans for example Volgs Clan. I can peace out with them but theres no dialogue to offer them to join the faction. But other clans can and I just want to know...

I offered the dragon banner to the Sturgian king. However, I decided not to support him anymore so that I could create my own kingdom, but that option no longer exists. Is there any way to create my kingdom after swearing allegiance and offering the banner to another king?