The player of the Psion has given you a perfectly acceptable reason for removing the PC... You told everyone to create heroic PCs, and he didn't. Tell him that, ASAP, before the next game, and that you want a new, Non-Psionic PC to join the party at the next game. Then stick to it. If (s)he shows up without one, let them sit and roll up the new one.
For the player who always interrupts, tell him/her to wait their turn, as others have suggested. If that doesn't work, try telling them that they're being rude, then go back to talking to the other PCs, coming back to them only when you're done with the first group. In all cases, let everyone know that being talked over is a problem for YOU.
If that STILL doesn't work, have angry NPCs start telling the PC "You're the loudest, rudest person I've ever met! Get out of my shop! We don't need patrons like you!" When the other PCs come in to take care of business FOR them, have the NPCs ask them "Why do you hang out with a rude guy like him?" If the PCs give a responce, have the NPCs shrug and reply "Birds of a feather flock together!", and start shunning the companion PCs, too... The peer-pressure from the other PCs might work, eventually, as more and more doors close to them. Have NPCs point to the loud, rude PC as he passes, whisper, and more and more NPCs shun him/her.
If all else fails, eventually have the Mayor, or whatever, come to the PCs, backed up with the Militia, and insist that they leave his town... When it starts up in the next town, the other PCs will probably solve the problem, for you, not wanted to be associated with the "rude dude" who gets them kicked out of towns!
Of course, if the loud interrupter changes his/her play-style at any prior point, this won't need to occur!
