Dear Walterbenjamin You are doing such a good job. Your DH's parents clearly had their own difficulties as children and young adults that they never resolved so these unresolved personal issues have resulted in a very difficult childhood for your DH. You are his rock. What hard work. Family is family and very valued so if you can still manage to visit etc. I think making things a bit shorter and perhaps learning a few suitable assertiveness techniques might help.
This pdf gives a brief introduction to assertiveness. You notice is says self care kit. You need one.
socialwork.buffalo.edu/content/dam/socialwork/home/self-care-kit/exercises/assertiveness-and-nonassertiveness.pdf
You might try broken record record - look for a fuller explanation. When you are refusing something ie a visit, you say. I appreciate that you would like us to do this... However we don't want to make that visit today. As they argue you repeat their main sentiment whilst finishing with your line: However we don't want to make that visit today
Also study what it is that goes so well in the first part of the visit. They seem to be a couple that must be engaged in activity as they can't cope with any personal chat yet if you didn't call they would feel they had lost their son.
Praise the stuff you like i.e. if you are served from a nice tea set that was a marriage gift say how lovely it is, how nice to see it again, lovely bone china so unusual these days etc.
If they discuss the weather you give them some further news on the weather i.e. a cooler/hotter spell is coming. If you want you could lead into what is the hottest spell they remember Was it the summer of? etc.
You might also try tactics such as having some knitting, sewing or tapestry to finish so that in their 'enforced' company you are always doing something. When they are being rude and controlling you would start to count your stitches, or thread your needle etc.
You could call these coping skills 'creative deviance'. Hopefully you will think of some more that will work for you. Good Luck!
Ann Droid, anyone watched this? BBC 1
Need encouragement in a difficult situation......


I grow all of my own veg as well as having a pretty flower garden - she never grows veg, yet she assumes this position of the knowledgeable critic on the basis of talks she has attended. So we will be in the greenhouse, and she will be bossing me around, even though she's never had a greenhouse herself and doesn't really grow from seed! I realise it sounds minor, but I feel like even the things I'm demonstrably good at are areas where she is constantly critiquing. 
