Guide to Influence Clan Relations
Once you enact your 1st law in the middle of the law tree, you will have access to the bonfire and canteen buildings.
Build these close to houses which are occupied by the clans you want to mingle and slowly they will start to hang out and improve their relations.
Alternatively, you can segregate the clans on different islands suing districts and peirs and their relations won’t change.
Hope that helps.