Help and advice urgently needed!

Meggie
Mummies of two or more close in age... 
I have a 15 month old who doesn't sleep through the night- he can be awake anywhere between once to six times a night, sometimes only for an hour but sometimes 3 or 4 hours 😴 
I'm due baby no2 next month! How did you or do you cope with both being awake and needing you at the same time? Do they wake each other up?! Any tips appreciated please! X