At what point were the missing party members lost? Did they appear in crust right after you left the maze? If not, you might need to restore from a save game before entering Curst.

If I recall, you can find a party member by either clicking their icon or hitting their marching order number (1 for TNO, 2 for character next to him, etc.) and then hitting "C". If they are in that area the view should move to where they are.
I hope this helps. Good luck.

In order to rest, your party members have to be close to each other - party being "divided" means your characters stand too far apart, even if they're in the same area. So if you enter the Traitor's Gate Tavern, leave your companions to stand at the door and go up to talk to Tainted Barse with TNO alone, you'll get that message when trying to order a room, because the area is large enough that standing like this is seen as splitting the group. Having even one character stand that far away will have the same effect. Just select your entire party at once (the "=" key) and take them all near the innkeeper, then talk to him.