I really recommend the book The Book You Wish Your Parents Had Read (and Your Children Will Be Glad That You Did).
There is a great section in there about how to argue. Some people who believe they are taking a calm, middle ground stance are actually being super passive aggressive or still trying to "win".
What I found fascinating about Perry's approach was it's actually all about feelings. About how you feel and acknowledging the other person's feelings. To an extent the facts don't matter.
I've seen all this in my family recently. Most have fallen out with each other and I've refused to get involved. Thing is they're all point scoring (or trying to) about "facts".
"You did x... then y..."
So what? Unless it was criminal, does it help the situation to tot up in some cosmic abacus on who has done more wrong? And each "wrong" was very much in the eye of the beholder anyway. Each had a spin on it with their own preconceptions and biases. Nobody shouted, nobody did the silent treatment but it wasn't effective and now it's all in this very frosty stale mate.
So my point is, it's not just about being calm, it's about recognising that the only things that matter are feelings. Because, for example, my partner is serially late. I used to get SO ANGRY with him for it before I accepted this was an inevitable part of his character and all getting angry was doing was getting me riled up. So now I expect the behaviour I get and I plan accordingly. The behaviour hasn't changed but my feelings have. So there's no point getting mad about something I'm not. Likewise, if he does do something which frustrates me and I do want to try and change the behaviour, I start with "I feel..." or "I felt..."
So for example, "I felt frustrated that I did all of the holiday organisation last year because it put pressure on me in a way I didn't have headspace for with how busy my business is."
This year, he's booked the holiday, without being asked. First time ever. 👍