I remember that. A newborn who didn't want to sleep, no matter the hour, and parents so far into sleep deprivation that the only thing that mattered was sleep. I'm not sure how a baby that's supposed to sleep 18 hours a day can be awake all night, but... it certainly seems that way. Looking back, trying to make a baby sleep is like pushing a rope. It only works when they want to.

If you can, tag team. For at least a while, let the baby's sleep schedule be what it is, and just hand off every few hours so someone can sleep. If that's in the dark hours, great. If not, you'll be tired enough anyway that it doesn't matter.