sure you can do it, all you do is connect the wan port from router 2 to lan port of router 1 - then the wan from router 3 to the lan of router 2
what you are doing is adding in extra layers of NAT, which will work, but a little messy.
you could connect wirelessly to any router if you wish
i assume the problem is how to physically connect the routers.
the description about is assuming you are doign all of this wired,
but, if you want to do it wirelessly, it get a little more tricky.
first router #2 & #3 havr to support wirerless bridging or repeating (check spec)
if they do, then your in luck, bridging woudl probably be thwe easiest, all you havr tyo do is enable bridging on the router and enter the same ssid / channel / encrypotion (only wep I'd say) on router #2 & #3 - and enter mac address detaisl on either end of the bridge.
once connected the bridge will be wireless, yet produce you wired connections on the router 2 & 3 for your other devices.
its a little tricky to get right...
before trying anything, check you hardware can support wireless bridging, if it cant then all you can do is do it wired as above.