HopeCA - just chiming in very quickly to say that in my experience, boundaries aren't really boundaries if you have to get someone's agreement for them, or need to discuss them, or need to bargain for them. You just live them. Boundaries are what happens through action, rather than conversation.
I've begged and pleaded and threatened and all sorts in an attempt to get H to stop verbally abusing me. It never worked. So now, I just don't talk to him. We exchange pleasantries at the door if he's in a civil mood, and if he isn't, I ignore him, make a fuss of Youngest, and close the door on him with relief. My boundary is 'I will not be in conversations where I am not spoken to with respect' and I am just living it, rather than trying to get him to participate in it.