DeMarco and Lesedi's Arrival
DeMarco and Lesedi Singh — The Pirate Lord's Children — were given a map by Old Belanger to a treasure left behind by their father somewhere in the Sea of Thieves. This kickstarted a race between the two siblings to who could find this treasure first.
After a lengthy campaign, both of their crews arrived at the same island. There was a scuffle between them, but they managed to dig up an elaborate chest which contained the other half of the pair of cursed pistols. After a brief encounter with The Gold Hoarder, they agree to work together thereafter.
Source
Sea of Thieves Vol. 1