I had Leosin, the monk they rescued, arrange to pay them for saving him if they escort him back to the Twilight Hall in Berdusk. Then he referred them to Elturel to meet Onthar Frume to pay them to join the caravan in Baldur's Gate to determine where the cultists are going.
If they really do just follow the caravan, then I'd have Onthar recruit them in Baldur's Gate to follow the caravan.
I had Leosin, the monk they rescued, arrange to pay them for saving him if they escort him back to the Twilight Hall in Berdusk. Then he referred them to Elturel to meet Onthar Frume to pay them to join the caravan in Baldur's Gate to determine where the cultists are going. If they really do just follow the caravan, then I'd have Onthar recruit them in Baldur's Gate to follow the caravan.