Legends - "The Skullduggers"
Rare7.8%ObjectiveOptionalMulti-player
You played the same shanty in a band of five Pirates.
What it says on the tin; stand in a group of 5 players and all play a musical instrument at the same time.
But, the bit that makes this harder is 5 players, and there's a max of 4 on your ship. So you need to be lucky with a friendly crew at an outpost, or in an alliance with one. Chat/voice comms to request everyone goes to the tavern for the achievement definitely helps.