Assign low priority to mobile devices, apart a few execeptions

This is your choice. If this is the preferred method, you may follow the steps below.

  1. Ensure you are using Layer 2 managed switch.
    Configure Trunk port between Balance router and switch.
    Configure Trunk port between switch and AP.
    Assign Native/Untagged Vlan to all wired clients.

  2. Configure 2 SSIDs in the AP.
    SSID VIP = Untagged/Native Vlan.
    SSID Non VIP = Vlan2

  3. Configure Outbound Policies to route Untagged Vlan subnet to WAN1 and route Vlan2 subnet to WAN2.

Hope this help.