Your problem is either you connect the lan together behind the 2 routers and have DHCP conflicts or you disable the dhcp server and then only 1 router is really used. Your other option is to not hook the lan together but then it really doesn't matter what the lan addresses are. They can be the same different or whatever just like your neightbor can use the same ip. This will isolate them but then you can not share files.
You can not do what you want to accomplish with consumer routers. You would want layer 3 switches and maybe use something like VRRP to control the gatewy