I would plan the meeting with the Boars carefully. You have Kitsune's support, at least, and he is the heir; while he's safe inside Mitsumine holdings, you can be short with his uncle if he's disagreeable, or if the Boar envoys threaten you, you can sell him out. You might have to choose between having a strong ally sometime in the future and trouble anywhere from middling to severe now, or a potentially untrustworthy ally now, with guaranteed trouble if Kitsune survives to succeed the clan.