In typical ADHD style I wrote out a whole essay and decided instead, just to post this:
There is a point where you have to decide if it really matters.
Is the goal just to make them understand or do you need them to provide you with other support that only they can provide?
I also had a lot of trouble with both sets of parents.
I tried using examples of their own past behaviours and experiences. Things that had happened to their friends.
This worked somewhat. I don't think I'll ever make them fully understand.
Btw, I suspect my parents, my wife's parents and extended family all have ADHD.
On another note:
There is a chance your wife has ADHD as well, just different behaviours. It might be that there are things you do, that really trigger her.
I thought I was the normal person with the adhd wife. There was a strong hidden reason we got together and stayed together. It didn't become clear until later.