Were it me I’d investigate having the wireless links bonded into one interface (check out bonding). And the treat the rest of the problem as a transparent bridge between the local LAN interface and the bonded interface.
I would not try to use the load balancing and failover logic which is designed for routing between multiple ISP links. Bonding supports load balancing failover at the Ethernet level below the IP level. For that reason a single TCP connection can be balanced between the links. If you use the TCP level load balance and failover you lose that and each TCP connection will be constrained to a single microwave link.