Even the biggest 747-400's do not have "passenger lounges" in that
upstairs space.  The purpose of the additional room is for more
passengers, not so the coach or first class people can go up and hang
out and have a drink.  That would not only be dangerous, but it would
be a huge waste of space.

The only jet which may have a piano would be Air Force One.  From the
747 double-deckers I've been on, that has always just been used for
seating, and business class at that.  First class is in the front, and
the cockpit is on the upper level.

Damon Atchison