If your modem has 2 lan ports and is also a router, then yes, you can.
If you want the systems on the same network(and your DSL modem is in fact a router), it is best to disable DHCP in the the other routers to allow the modem/router unit to assign ip addresses. Please note this turns the router and wireless router into a switch and wireless access point(you do not use the WAN ports in this configuration).