Calais is an inconvenient place to meet. There are two station, Calais Frethun and Calais Ville.
You need to get from Brussels to Lille and wait for a connection to one of the two Calais stations.
Calais is a particularly soul-less place, just a port to cross the Channel.
Is there a reason you want to meet there? Lille is much nicer, easier for you and probably easier for the rest of your party. Where are they arriving from? Is this today or a different day?
Taxis in Calais? I don't know, but I have not heard good reports about getting around in Calais. There are buses. Where in Calais do you need to get to by taxi?
I am there many times a year, by my own car, and get straight out of town.
By train it will take you around 2 hours, with around an hour of that waiting in Lille.