Maybe instead of allying with another faction, it's allying with another clan and helping to found a kingdom. You know the blood covenant and the division of the land in half.
Therefore, an editor of sandbox characters and some form of story would be interesting. For example, they swear a beautiful wife and you are tasked with helping the clan conquer a settlement and then create a kingdom, and here you can choose between two kingdoms or one strong one. It would be interesting to be able to create such a story and a second clan. As for clan members, I don't think wanderers should be counted as they don't have blood ties. Unless there is an option to reform into a noble family.
If they have a problem with creating a cooperation, let them add an npc that they will create for themselves with more possibilities related to it. (Npc would work independently to make decisions. (I don't know how far it is possible) E.g. we call him for help or something.)
More paths of choice with possibilities like three paths in cyberpunk.
Like the legend of the three brothers. Lech, Czech and Rus who split up and founded other kingdoms.