Feeding before bedtime is a big part of it. They will sleep much longer, because of their basic needs being met. I had twin boys only two years after my first son was born. The twins did not sleep through the night unitl they were nine months old. And of course if one woke up, so did the other. I do recall sleeping in the recliner, one son on each arm with a bottle in their mouths. (And me wanting a good drink too, but no, I did not)
That time was a blur for me, I worked third shift fulltime, was going to college fulltime, and was a very active member in the National Guard. I really do not remeber much of any of those first nine months other than constant fatigue.
Feed the child. Fresh diaper, It will make life much easier for all.