When somebody connects to a wireless access point, their communication happens only through that access point. If you want to communicate with a member of that network, you must get the access point to route/forward your signals to that device. To do that, you must be part of the network; in other words, to associate and get authenticated by the access point.
So, no, you cannot port-scan the devices inside that network unless you somehow create a network with them (some wireless ad-hoc network) or by exploiting the access point from the Internet (using its public IP address). For the same reason you also can't login to one of the devices using telnet or any other service.
As for spoofing the network, yes it's possible. You just need to use some social engineering, i.e. create another network with the same SSID and trick the others to connect to it. You might also do some trickery like pulling the AP's power plug so the other users will only have your network to connect to.