Crying baby and miserable neighbours

I would probably go and talk to them as things can get passive aggressive with messages, explain that you’ll do what you can to save the baby but this is just a phase and there’s only so much you can do…

X

So you live in an apartment

Me being petty I'd post the letter back saying to shove it up her ass considering she's complaining about a baby and wants to not sound like a complete asshole so she's giving vague examples of regular household noise.

If you have a landlord, manager or someone you can go to about this, I'd go that route. Or you can make another letter apologizing but standing firm that the baby is a baby and there's nothing you can do besides what you are doing and some babies can be colicky and unfortunately there's nothing you can do about that besides patience and understanding.

Or you could try to have a convo and record it and then if there's another complaint or she ends up being a dick again, you can send everything in to the landlord or management for harassment and or bullying of a minor.

As for the noise issue, you can try to find things that help reduce sound, find music the baby can calm down to or see if a vacuum works (it does for my youngest).

Hopefully this helps a little.

I understand the suggestion to tell her to shove it but you are the one living next to her, so better not escalating things. Maybe invite her over for a coffee , explain the situation, if you feel safe to do so, introduce your baby to her. Sometimes being friendly can help smooth this and she would feel embarrassed for sending you this letter.
Does she lives on her own? Is she a mum? Or older women? What is your current relationship?

Tough shit for your neighbors. Babies cry. If they don't like it they can find a home without an attached wall. I lived in an apartment and an attached town house before and all the neighbors were extremely loud. Its just part of sharing walls.

I would not confront her if she is frustraited with you already, just ignore her, it May be a short phase and she is probably one of Those Karen’s that complain about everything anyway.

Defo don’t go round and apologise for something you cannot help, and neither can your baby. Unfortunately the neighbour will have to put up with it, spend some money on some earplugs. As babies cry. Cannot believe there’s people in the world that would actually think it’s acceptable to post letters through peoples door because of a child crying. X

Let me help you write a letter telling them to f*** themselves. Don’t even worry yourself, babies cry. But your neighbours can stop being a Karen.

If my neighbours tried such a thing, you will see me on crime and investigation.

Ok so the problem is not just the baby crying, but you already have a broken relationship with them due to the renovation and maybe something even before that?. The question is, do you want things to keep escalate telling them to f** off?. My 4yo still wakes up crying or screaming because of nightmares sometimes. I'm in a semi-detached too and did renovations, we fortunately have great relationship with our neighbours and talk to each other if there is anything.
I also gave chocolates to a neighbour that allowed our builder to access his garden during our works, we barely knew them.

All this to say, you are the one who are leaving with the stress of "disturbing" your neighbours, so better trying to reconcile than escalate the situation imo. Otherwise try to ignore them, but it seems they can come to you sending letters or talk to your builder no issue, so that won't stop.
Also don't spend money on trying to rearrange the room to make less noise, the core problem to me is your relationship with them that need to be fixed