These people have to be real people met through Wi-Fi connection.
If you have two game consoles and two games, bring them both down to the underground and you should be able to see each other.
There is a trick to the Spiritomb thing - apparently, if you consecutively go down to the Underground, interact to the person, and go up, and consecutively do that a number of times until you get Spiritomb.
Remember, actually talk to the person. :3
Hope I helped. :)