Powerline with Wi-FI extender not working well with 2 WAN router - eviltoast

Let me explain my current setup so that I can explain the problem…

For redundancy, I have two internet providers at home. One of them is DSL and the router is located at the entrance hall. The other one is cable and the connection point (and therefore the modem/router) is at the living room. My workstation is in another room on the opposite end of the apartment.

To connect all that, I bought a set of powerline adapters from TP-Link, one with 3 ports and WI-FI extender and two with 3-ports alongside with a load balancer multi-wan router, with 5 ports also from TP-Link.

Right now, I have one the multi-wan router connected to one powerline adapter (one port for each wan), another adapter at the entrance hall connected to the LAN of the DSL router, and the adapter with Wi-FI extender connected to the Cable router.

The wired part works. My workstation connects to the router and I get an IP from it. The router can connect with both WANs and my connection seems stable. My problem is in the wireless part. From my phone, it says it is connected but it can not resolve any external connection.

At first I thought the wi-fi was getting confused with the different DHCP servers, but even after disabling DHCP on DSL/Cable routers (not using it anyway because I am connecting through the “multi-wan” router, right?) the connection is still not going through. I can access the management part of the Wi-FI extender and it seems to be on the same subnet as the multi-wan router, so I guess it can connect to it, but the actual connection outside simply doesn’t happen.

Is this setup so out of ordinary? Should I just forget about the wi-fi extender and add a “real” access point in the living room? I guess I could accept that the mobile devices need to be aware of the separate WAN routers, but it would be a lot nicer if they could all connect transparently…