I can only share my story: When my wife wanted the divorce she acted a little like Dan from the "no lawyer, you work it out point". I didn't want this divorce and you know that. But, it was important for me to make sure my children were protected through all of this. She wasn't prepared to make the right decisions (e.g., no money etc) and so I took the lead to make sure she was protected and my children would never see her suffer.
I think your case has some similarities. Dan isn't in a position to do this right. He needs someone to help him and he won't get help on his own. My fear is that if you let him try to do this on his own it could be messy and ugly. You've seen what happens when he gets really upset.
I know you don't want to be the one to file and neither did I. At least in my state we had the option of filing jointly. It's the option I chose that let me sleep at night and still protect my children.
Just my two cents....
You are the sane one. You need to be the quaterback right now BBJ. I know it sucks. But I also have complete confidence in you. You are a strong and special person. Afterall, you are my little sis. I don't expect anything else.