I'm really getting a strong feeling that those posters saying 'this is all over nothing' have NO real life experience of toxic families.
Because it seems those of us who DO Know exactly what will happen if op & dh give an INCH at this point. Which is
A op & dh will NEVER hear the end of it. EVERY Minor disagreement this will be thrown in their faces.
B IL's will see it as a huge win. And as a green light to try and exert more control
C the next time such a situation arises it will be MUCH harder for op & dh to deal with because the IL's will be even more stubborn because in their minds they gave in the last time so they just need to dig in until they give in.
D the next time could well be when baby is here, when op&dh are also dealing with all the demands of parenting and depleted emotional resources. Which also makes it much harder.
It is NOT the same as dealing with normal healthy parents.
My parents are the toxic ones. When I was married my IL's had a very different relationship in their family BUT because I was used to what I'd been raised with whenever there was a disagreement, misunderstanding I got SO anxious because I (naturally given my upbringing) feared it would escalate into a huge row with awful things being said and people getting really hurt.
"NC should really only be for people that are dangerous/addicts/you feel will harm your child." Such behaviour IS harmful/dangerous.
Emotional abuse is JUST as damaging as other abuse (and believe me I've had it all!) it has long term serious effects.
Ghetto is right too. Going Nc if problems persist avoid/reduce mh stress rather than add to it. There are MANY posters who say it was a tough decision, took them a long time to get to that point BUT it ended up being the best thing they ever did.
Also I'm probably a similar age to the IL's AND I worked in elderly nursing for several years and had relatives with different types of dementia - and the dementia thing is nonsense! It's very rare to develop it so early PLUS op has been clear he's ALWAYS been like this. That does not indicate a new/recent medical issue at all.
Op is right to follow dh's lead on this. He knows them best especially as they've likely been putting on a 'best face' for op.