Triumvirate Treason was the name of a group of three Privateers who mutinied, but are still considered Privateers.
It is easy to tell the three from the rest of their crew, because of their blue jackets. All three come with the crew collection.
Charlie-- Leader of secret Triumvirate Treason gang, searching for the finer things in life.
Bartholamew Jackson-- Devious Triumvirate Treason strategist with a taste for fish guts.
Stevedore Springfield-- Easily angerd weapons master for the Triumvirate Treason gang.
All of that came from the official Crew Collection set.
Lockpick Cabot from Smugglers Fort 2.0 is a Privateer also with a blue jacket but he is NOT part of the Triumvirate Treason.