About the vitamin D. It's involved in methylation and when we ran genetics recently my ds turned out to have a defunct vitamin D receptor gene. Methylation issues are SUPER COMMON in autism, and vitamin D is part of that. We put my ds on niacin to bring down his methyl levels (which we know are high for his mix, not saying you should do that) and the vitamin D to stabilize it. Wow, huge, huge, huge changes. So much of the aggression and destruction and volatility is gone. The D is really key for stabilizing him, totally miraculous. So it sounds way too simple, but it's not crazy. Run the genetics and see, kwim?
As far as your dh and the grief, well he can't process it if he doesn't know he's feeling it. ASD involves a lack of self-awareness. So he doesn't realize how he feels, so he can't even begin to process it. Personally, I would assume he's on the spectrum and treat him as such. He's either kissing it or all the way there.
No, the talk therapy sounds worthless for you right now. Bringing in a BCBA, that would be huge. Solving physical problems (D, methylation, etc.) would help. We've had some significantly rough patches, and for us no ONE THING was the answer. Like we needed the ABA *and* the methylation work *and* this and that and more. For somebody to say well a BCBA bringing in ABA/VB would solve the behaviors, well that's not acknowledging that my ds really needed some physical help to get there.
On the dysregulation and behaviors (you said she ruins an activity, for instance), does she have a place to go to take breaks? She needs to take breaks. Enforced breaks. Breaks before she gets that uncalm. We worked for a year on how to take breaks, because for everyone to stay safe and calm and not have behaviors like that, we need to realize we're going yellow zone, realize we need a break, be able to say I need a break, and leave and go to your break space and then return.
That break thing took a long time for us. When we started, one incident and ds would be gone, toast, for hours. Now he's like 90 seconds. But we worked on it hard, a long time. And we didn't go for the gold on breaks all at once. It was in steps, like we're actually going to tell you you need a break and physically escort you to the break space. Later tell you you need a break and you go do it. He would bolt from the room and we ignored that part, working on language, till eventually he could maybe use his language. You can use visuals. You can model it yourself by saying Mom needs a break and going and taking a break.
That's your ABA/VB kind of stuff a behaviorist can bring in, helping you problem solve. If you can get one you like, someone you can talk with, it would be worth your time/money. It would cost less than your unhelpful family therapy, and the person could actually be in your home, seeing the issues for themselves.
Fwiw, on the hair, we have a gig in our house that everyone does it ONCE. Like you probably did it as a kid, I did, etc. We just said Hey, you've had your once, now don't do it again. Kids are curious. Because, honestly, of all the things to blow up a marriage over, this is so not the best one. Like really, let it be something major. The hair thing is just normal kiddishness, honest. Kids do that. As long as they only do it once, we're good.