When players reach Act 3 of Baldur's Gate 3, the two remaining champions of the Dead Three will approach the party and offer to work with them in exchange for getting rid of the other one. Players are free to side with Orin, Gortash, or neither, but players will need to find a way into at least one of their strongholds.
Baldur's Gate 3: Investigate the Murders Quest Guide
If players want to reach the Temple of Bhaal, they first need to figure out what to do about the string of murders in Baldur's Gate.