If it helps, write down what you want to say to her and when you're ready to tell her, read from the script. That way you will only say as much as you want and you won't get sidetracked by her unpredictable response. I may look a little formal, reading from a prepared text, but at least you'll be able to stay on task.
When telling the kids, you can be more natural and just speak from the heart. I would tell the kids, then go right to W and read your text. Then maybe go back to the kids and tell them you told her so they can prepare themselves for her reaction.
M: 59 W: 53 M: 9 yrs T: 14 yrs No kids together but D30(hers), S27, S24, D21(all 3 mine) W moved out 11/18/2013 D-Day 12/14/2013 W moved back home 12/1/2014