Please please please take the papers to a solicitor. If you don't want to physically read them, get them to. You say you did it not to upset the children, think long term here.
Learn to remove yourself from a heated discussion and stay calm. Do this for the children and for yourself. You can always walk away and say, 'lets discuss this later in private. I shall go out for a while till after dinner' or something. Get away from the situation. She knows how to manipulate you and is taking full advantage.
I'm so sorry it sounds like hell there at the moment. Take Saffies advice, go to a solicitor.
