you can't get rid of Varric/Aveline/Merrill/Anders, not ever, so that's a letdown too.
I've heard that you can actually ask Anders to leave after the resolution of his personal quest in Act II if it ends a certain way. This doesn't actually change what happens at the end of the game, though.
The other three, yeah, I'm pretty sure you're stuck with for a while. I think you can get Merrill to turn against you if you just don't have enough friendship OR rivalry and you pick a certain side. Same might, might, might go for Aveline but don't quote me on that.
Varric you're stuck with for life.