It doesn't sound like an out of control party. Not being able to find your belongings is typical of any party or get together. "Mom, I can't find my shoes." Heck I can't find my purse most days and I'm sober.
Are the kids traumatized? No, but I don't know for sure. They might. Hurt and confused. Probably and that's just not cool. I can't believe how HE acted either. You and your husband can't believe how HE acted either. It's understandable that you uninvited him.
Hosts don't scream at their guests and let them leave dripping wet. A good host would help find the towels. Something is wrong with this guy. Her family knows it. His friends know it. You know it.
Are you wrong for uninviting him?
It's your party. Sadly, under the circumstances, you felt you had to. But under the circumstances, I know there is no way she would have come if he was uninvited and it would have blown up. For him, it's a matter of honor to prevent his girlfriend from going also. You didn't realize that.
Of course she is upset about this. It IS insulting (too bad - bad behavior has real life consequences) and she's the one who has to deliver the news to her angry boyfriend "you aren't invited anymore." So he goes into a rage and what is she supposed to do with the anger and venom he spews at her? Break up with him? No. She "can't" because she's very bonded to him already (premarital sex does that). So she will take it out on the last friend she has. And blame your husband.
He's managed to anger her family and push them away. Oh great.
It would be nice if her family could have an intervention and sit her down and talk with her. She will not be "happy" if she stays with him.
What should you do now?
You tried talking to her. She can't believe you and your actions.
Whatever. Let this go.
You can still be her friend, but for now let this cool off.
Hopefully she'll get a clue.
She will probably cut you off, but you can't control that.
If she comes back to you, be there for her. She may cut you off, but you don't have to cut her out.