router config for 8 unit rental complex

I recently built an sold a small vacation rental complex. It has 8 units and needs WiFi. 90% of renters will be Oracle employees so security is a must. I setup a new Dlink N band router and it works fine, but the users have to go into “internet Connection” in XP to set up the connection. This is not going to work for most. Is there an easier configuration to use that will allow them to just enter the SSID passphrase and be connected kind of like you do at Starbucks or McDonalds. Using WEP 64 now as security. Will there be a problem if 12 users log in at the same time? Any info is appreciated. Thanks