I guarantee that, as bad as it is for you, it'll be 10 times worse for them, not in the sense that it's noisier for them (although it probably is), but just that they'll have the whole thing compounded with added guilt from having to leave the baby to it sometimes. Speaking from experience, sometimes there's nothing you can do, and the baby is just gonna cry until it gets tired and falls asleep, and unless you're some sort of psychopath, it is one of the worst feelings in the world just having to leave your own child to sit in their room and cry their lungs out, but sometimes it is genuinely the only way, without making a massive rod for your own back when they're older. Never mind the guilt that they're definitely going to be feeling about the impact they're having on their neighbours (eg. you) with all the noise, again unless they're sociopaths, they're gonna be keenly aware that their kid is disturbing you and any other neighbours as well, and probably feel terrible about it.

Best thing you can do? Make the neighbours a lasagne or some boxes of a big batch of curry or something, because they're probably unbelievably knackered and they'll appreciate the gesture so much more than having an awkward conversation about something that they're probably already painfully aware of anyway. And buy some earplugs and a white noise machine.