Welcome, LD0810.
I don't think you are violating any rules here - there really are no hardfast rules except this one: are you prepared for whatever consequences may come from talking with his children?
It may not go over well. They are his kids, after all. And I know with my Mom and her mental Illness, my Dad tried to talk with us for a handful of years and none of us siblings wanted to see the serious issues he was bringing forth. Plus, she made him out to be the crazy one for a while, and was very effective at it. I'd say it took me several severe bi-polar episodes that I got to witness firsthand before I was able to agree with my Dad.
So what if you simply addressed the damage its doing to your marriage by speaking to him directly, and finding some support for you? I know there are Al-Anon meetings in Ireland...