Here is the full list of all 11 The Grand Ball achievements. It takes around 0-1 hour to unlock all of the achievements on Windows.
Opted to help the Margrave
All Endings
Took it on yourself to seal the leak
Reached the end and shook hands with Alfred
Ended with the Duchess of Cumberland
Romantic Ending with Eliza
Caught with Earl of Doncaster.
Romantic Ending with Christine
Went on the crazy night hunt
Declined Jameson's assistance
Arrived at the ball.