I need help with how to handle this from people who can think straight.
NDN have 3 DC, 2 of whom have ASD. Their middle child is easily overwhelmed, and when he's not coping, he shrieks and bangs his elbows against the wall. Their youngest (no SN) is very prone to tantrums (the on the floor, screaming and throwing things kind). We've always had a lot of noise through the wall and from the front garden (shared path) through the day, and on a night if you're awake with no TV on, you can hear if he's having a bad night, but nothing that's caused us any bother really. The worst is that on the increasingly rare occasions DS naps, it wakes him, but an early night is enough to remedy that one.
Recently they've swapped around the bedrooms, so now their middle child's bedroom shares a wall with our house. for the past 8 nights (since the swap) he's been awake for the majority of the night, screaming and banging against the wall. DD (5 months) sleeps through it fairly well, but it wakes DS (2). I can't sleep through it even during the windows where both of my DC are asleep. I'm going to make an assumption that on account of the lack of sleep, their DD has been throwing tantrums left right and centre, including on the bench under my front room window, which has woken DS when he's trying to nap throughout the day.
DS is tearful all day, and actually fell asleep on the floor in the library yesterday as he's exhausted. The cherry on the top was my neighbour from the other side making a snarky comment as we were on our way out yesterday about my kids being up all night crying (their bedroom is on the other side of the wall to ours).
I know I can't dictate what they do in their own home, but is it too CF to ask if there's any way they can switch back? I REALLY don't want to be an arsehole over this; it must be so difficult managing their needs, and it's not a noise they can help making, it's not like their choosing for their children to be distressed. On the other hand, I'm exhausted, my kids are exhausted, and I don't see this ending any time soon.
You can hear the noise equally in all of our bedrooms, and it's not much quieter downstairs (I come down to feed DD if DS is asleep to avoid disturbing him as she often has a little chat before going back to sleep). We looked into sound proofing, but even doing a "cheap" hack it will be several thousand pounds to cover the expanse of wall which would need doing. We've tried disturbing the sound by putting the air purifier on the landing so it's between the noise source and us, which has helped a little, but not enough. We can't afford to move (we only bought this place in August).
Any sensible ideas?