There's not much I can add to Sandi's EXCELLENT advice, and I'm in a bit of a rush at work this morning, but I did want to add this:
You should have called 911 when your wife threatened to cut herself. "A", she needs help, and "B" you will have established both a police and a medical file which will be useful if there is ever a 2nd attempt. You need to protect your kids right now, and if you're wife is willing to be some combination of not-well-enough and foolish enough, let her play into your legal hand.
All you need to say was "I was understandably alarmed at your behavior, and I'm not equipped to help you."
You're still protecting her, and she's going to continue to play that card until such time as she learns that it's no longer effective.
