@Hotblack
Hey
While I have not tried this before, I have a feeling this isnt going to work as you planned.. sorry!
In short the routers can likely only be used in normal wifi and not guest mode.. ill try to explain
When guest mode is enabled this stops the clients on the Guest WiFi going out into the LAN (normal wifi), the only place the guests are allowed to go is the internet. In a normal one router setup, the guest connects to the guest wifi.. his data goes to the router and out to the internet. In essence it cant "mix" with other traffic on the network. With this in mind its likely blocked from going out any of the LAN ports, as it would literally have no reason to do so.
This is your issue i believe..
The older routers can enable Guest WiFi, however the only way that data can get to the internet is via a LAN port mixed with the other 'normal' wifi traffic... therefore the LAN port is blocked to guests, therefore it wont work. Unless this router was directly into the internet connection, its got nowhere to send the guest data.
Guest WiFi would likely work on your main router only, as this can go straight to the internet.
If you wabt guest wifi all around the house, you are into VLANs (virtual lans) to seperate the guest and normal user traffic. This is outside the requirements for Home Grade devices, you would need to invest in something like the Omada EAPs to do this. EAPs are advanced Access Points capable of doing what you requested.
Hope that helps... :)