[X] Plan Give Him Options
-[X] Off him the choice:
--[X] You hold the keep in trust until you have found out what the Illithid might want from him. You privately recognize him as the Lord of Kayce, but won't do so officially until you can guarantee his safety.
--[X] You name him the lord right here and now under the condition that you will station your own servitors there, Inquisition, undead and flesh-forged mostly. Make no mistake, Kayce would become a trap for the Illithid and everyone within would be bait.
-[X] Either way, you would ask for his participation in some research to figure out what they wanted from his family as it could be helpful to defend the realm or at the very least to better predict the Illithids movements.