The Winter Knight also joining as a freeholding lord would be kind of a balance issue with Summer.
*Maybe* the Paranet could sign, with him and Elaine as heads, but the Paranet doesn't have a whole lot of street cred for fighting ability outside of Harry himself, considering Elaine has been sandbagging to keep her true ability secret. The organization signing the accords might attract attention from challengers, and that would put the little fish in exactly the kind of danger the Paranet is supposed to help them avoid.