My wife and I have four, 8, 6(twins) and almost 5. Zero to four kids in 42 months.. Obviously having twins and a kid who just turned two the month before was a nightmare. The stress about took down our marriage, I basically have blocked almost all of that time from my memory.
No help from grandparents at all. I talked to my parents about it a year ago and my mom actually bragged 'Well we did watch all four while you picked up your wife from getting her tubes tied!'.. yep she bragged about watching all of them for 30 minutes, wouldn't even watch them long enough so I could stay with my wife during the procedure. We've had two nights alone together without kids in the past 8 years(we had to pay my in-laws family.. I shit you not). That may change as they are getting old enough for a sitter now.
We still have someone get up almost once a night with a nightmare or some other issue. We get maybe one or two days a week without anyone getting up. All four are also early risers, up at 6 to 6:30am every fucking day of their lives, doesn't matter what they did the day before or how late they stay up. This morning my wife and I slept in till 7:30 it was a fucking miracle.
Also we have found their are 'good/easy babies' and 'hard babies'. Our youngest was a good baby, so easy, sleeping through the night in a just a few weeks, our oldest three were very tough. So hope you get an easy one.
On the plus side my eldest son is a good Terraria player, although he is a loot whore.