Общие:
Are the crew members thinking about their Christmas holidays?
Aren't the crew members thinking about their Christmas holidays?
Альтернативный:
Are the crew members thinking or planning their Christmas holidays?
К подлежащему:
Who is thinking about the Christmas holidays?
Who isn't thinking about the Christmas holidays?
Разделительные:
The crew members are thinking about their Christmas holidays, aren't they?
The crew members aren't thinking about their Christmas holidays, are they?