First pregnancy recently announced. PIL are well-adjusted, sensible and kind people who read social cues well. They are absolutely delighted about the pregnancy, and will come to visit the new grandchild briefly after the birth. They have said they'll definitely stay in a hotel, turn up, say the grandkid is wonderful and parents are doing brilliantly, bring cake/ takeaway/ nappies/ whatever, cook a meal if we want it, and not outstay their welcome. MIL has offered to stay for a week longer "to provide female support" and to cook meals/ help round the house. Sounds great to us - she is generally kind and helpful, knows when to offer advice and when to shut up, etc.
So far so good.
My parents are generally messed-up, selfish, angry, petulant and vicious. My mother can read social cues enough to know how to put on a "nice" social manner when required - terribly polite, fulfilling all the requirements of a perfect 1950s hostess, but full of barbed, bitchy comments and attempts at triangulation. Her level of social insight is not particularly high. My father is frankly just boorish, arrogant and rude. He can read social cues fine when he wants, but is almost always too selfish to give a shit about them.
They have made it clear over the years that my mother never wanted me, they both hated the experience of having a second child, and that that was my fault because I am an embarrassment to them because I'm "weird" and "retarded", "have no taste", "can't run my life like a normal person", etc. They think "people like me" shouldn't be allowed to have children, and should have them taken away. My mother's evident PND and inability to ever bond with me is all apparently my fault.
Since I announced I was pregnant a few weeks ago, they have only said congratulations once, gracelessly, when in the company of other people - and the three attempts I've made to discuss things like visits with them have been met with very rude "we'll do what we want, when we want, and you aren't going to tell us what to do, and we're not going to discuss it with you, you're incompetent and embarrassing" responses.
Well, OK, they're not going to be involved grandparents...
However, i know my mother well enough that as soon as she realises that MIL is going to be over here providing support, all hell is going to break loose about why mother was not invited instead, and why we say "no thanks, we do not need you to come and stay". My mother has talked to PIL and played the interaction well enough that PIL currently think the only issue is my father being boorish about it all. PIL do not understand just how bad the relationship is with my parents, and aren't going to respond well if we tell them (PIL are big on mutual respect and politeness - generally great- but that extends to being unable to cope with people who have poor relationships with parents).
How on earth do we deal with all this, in a way that minimizes the stress and maximizes the benefits of good relationships with nice people?