[svandamme]

Routers can have the same IP , as long as they don't share the same network.

Lets say Router 1 has Internet IP 10.5.1.30
router 2 has Internet IP 10.5.2.45

Both can have the internal IP 192.168.0.1 and assign ip's in that range to devices on their local network.

If both want to be on the same internal LAn, then both will need a unique IP on the inside as wel. for instance 192.168.0.1 & 192.168.0.2

But one would have to be the Master that does DHCP, and the other one would need DHCP server disabled.

Unless they is fancy routers that know how to work redundanty But that's a whole other story