When completing the First Light questline in New World, eventually Sylvia Oakes will give you the One Threat At A Time quest.
She asks you to defeat Boatswain Ambrose and Quartermaster Zebulon at Nyhart's Anchorage.
Where to find Quartermaster Zebulon
Finding Zebulon is pretty easy -- he's on the ship at Nyhart's Anchorage, at the blue marker on the map below. Simply battle your way on board, and take him down.
Don't forget to check the ship for valuable Supply Crates!
Where to Find Boatswain Ambrose
Boatswain Ambrose is a bit more hidden. Instead of looking for him in the huts high up in Nyhart's Anchorage, instead stay in the beach and follow the base of the cliff.
He's located just below the location icon on the in-game map -- underneath the huts, in a small cave protected by a few mobs. This is marked by the red skull icon on the map below.
Check the video above for specific locations!
How to defeat Boatswain Ambrose and Quartermaster Zebulon
These two pirates can be tricky to kill if you're alone, and it's recommended you're at least level 17.
Given the pair are both Lost (undead), they're weak against Nature and Ice damage, as well as bludgeoning weapons such as the War Hammer. On the other hand, you can also use piercing weapons, such as the Rapier, Sword, Bow or Musket.
Statistically, Nature damage works best. You can get this by using a Life Staff, or by socketing your weapon with Amber. This converts a portion of your damage output into Nature, helping you take down the Lost quicker.
The Aquamarine will grant the same for Ice damage, and of course the Ice Gauntlet is useful.
Building the Lost Bane perk into your weapons will also increase your damage against the Lost. This is done by baking a Riveted Orichalcum Mail into your weapon when crafting. Arcanists can craft Lost Coatings, which grant temporary bonuses.
While not particular tough, both pirates hit hard. Dodge their heavy attacks (when they glow white before striking), and consider a block-and-counter strategy. Just as they strike with a normal attack, hold your mouse button to charge a heavy attack, then block again. This should mean you take less damage overall.
Of course, make sure you clear any mobs beforehand so you don't get swarmed, and bring plenty of healing items just in case!
Map Image courtesy of MapGenie.