Hey! Just in case you want to know: _die Nacht (the night) - feminine _der Morgen (the morning) - masculine
But, we have to use the accusative and say "Guten Morgen" / "Gute Nacht". Why?
These phrases are the short version of: Ich wünsche dir einen guten Morgen (I wish you a good morning) / Ich wünsche dir eine gute Nacht (I wish you a good night). That's all folks!
I said, "Good morning, how are you all?" to mark the plural distinction that modern English grammar does not formally have, and the owl took away a heart. I think that it, along with "Good morning, how are all of you (doing)?" (which I think might even sound a bit more natural), should be accepted as possibilities.