Marker is used as currency for services in the Rogue Harbour.
Gather Markers. You’ll get these from regular monsters throughout the game and from turning in Artifacts after you complete Heists. These are essential for paying Rogues to assist you with Heists, and to reveal details of a Blueprint for Grand Heists.
Markers are fairly common. They can be dropped in stacks. You’re currently able to store them in stacks of 10,000 in your inventory and 50,000 in your stash.
Yes, the standard party rules apply here.
No. The only types of content that have auto-pickup functionality are things that are non-tradeable like Metamorph Organs or Azurite.