The best setup would be to set one of the routers as an access server,
If that is not possible, you can do port forwarding on the 800 series router to telnet into the other routers.
Please have a look at this example, replace BVI with your WAN/internet port
http://portforward.com/english/routers/port_forwarding/Cisco/Cisco800Series/default.htm
Regards
Farrukh
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