My house upstairs also. Once awhile got crazy people singing on top of the lungs at middle of night 1130pm!
Last time when I am still working, got woke up in the middle of the night! My husband too woke up by the singing! He shouted upwards. But the singing continued...
I SCREAM!!! VERY LOUDLY! "STOP THE SINGING!" Then out of sudden, the singing stop for days at the middle of the night. After one whole week, very peaceful. Then one fine day, the crazy person who sing, or should I say "screeching the song" sing in another bathroom (kitchen's). At least not so bad.
Once awhile got drag furniture and drilling sounds in the middle of night. Morning is knocking knocking sound.
Maybe you can try go upstairs nicely say your baby needs to sleep. Not sure will work a not.