At what point in the game do you meet these characters?

Neera when you get to Beregost, Rashaad when you get to Nashkel, Dorn when you get to the Friendly Arm Inn. If I remember correctly Dorn's story doesn't start until later on though.

You have to talk to Dorn on the main floor of the Friendly Arm Inn. He won't join you then, but you will get a journal update about him. After you've talked to him in the Inn, you will meet him on your first attempt to travel to the Nashkel Mines.

Neera will run into you (and some red wizards) in Northeast Beregost. Rasaad is right in front of the Tavern/Inn when you first cross the bridge in Nashkel, both like jsidhu said.

There's a fourth character that can be found in an area somewhere to the west of the Friendly Arm Inn, but he will show up only after you gained some levels (I'm being vague on purpose)

if you want Neera without a fight grab Edwin first