As I recall, a seamen has a right to demand discharge and pay off when a ship is unsafe, I.e., out of class, or without a COI. Transatlantic has been under USCG detention for safety deficiencies for more than a month. The crew is unpaid since May. They have a right to sign off.
If the master is refusing to sign off the crew, they should report him to the USCG, and their union, MEBA, and they should add the Master personally as a named defendant in their lawsuit.