What you are doing should work. The wifi router will pick up an address from the ER-X, just like your laptop does. The only thing to keep in mind is the wifi router should be using a different subnet on its LAN side than the ER-X. For example, since you are using 192.168.1.1 and 192.168.2.1 on the ER-X, on the wifi routers' LAN sides you could use 192.168.3.1 and 192.168.4.1 or something.
Another option would be to turn off DHCP on the wifi routers if possible, and use them simply as wifi access points. You would connect the ER-X's eth1 and eth2 to one of the LAN ports on the wifi routers, rather than the WAN port, and the ER-X would give out IP addresses directly to clients in the 192.168.1.1 and 192.168.2.1 ranges.