i would consider installing pfsense on an old computer with a few NICs. you can do excatly what you want with 1 router/firewall (pfsense) and you wouldn't need the additional devices.
also, you can manage everything from 1 webGUI/IP address. right now, you have 4 devices you have the option to connect into. 3 of them being the routers you are trying to get working. i realize you already have the hardware and almost 100% operational, just giving you a suggestion. you may benefit (in the long run) from being able to manage everything in 1 location.