In Set Knowledge, you can enable if the knowledge you created is Public. If you leave the box unchecked, then I assume it's Private and only that NPC will know the knowledge. Public, I assume means every NPC will have access to knowing it. So you DON'T have to mod every NPC.
So, if I had to guess, and using your example as a means to explain it:
Your player character can be a new hire by slightly modding Darian by adding, "%NAME% recently hired someone new to help him guard Silverpine", to his Knowledge set. If you want your player to be related to Darian as a cousin, add, "%PLAYER_NAME% is a (optional: close or favorite) cousin to Darian." as another Knowledge set. Let the LLM put two and two together naturally and dynamically decide if he hired his cousin either as a coincidence or intentionally. Edit the knowledge if you want one or the other. Just make sure any lore about your player character's relationship with an NPC is NOT PUBLIC and increase relationship with them to whichever one gives you the key to their house so you can enter anytime and place a bed down to sleep. Probably Important, but if you're cousins.
