UGH...I doubt that an ad for online therapy was what was sought here. I have been thinking about the first post for a few days, and trying to think what would be most helpful. On the tantrums, I am guessing that there is some environmental trigger, perhaps that no one else can see/hear that is setting off the tantrums. It would probably be like looking for a needle in a haystack to figure out the why, but there is usually a reason.
I was also struck by him being out of control in kindergarten. Is he in a mainstreamed classroom? Does he have an aide? Sometimes the most ordinary things can be overwhelming for someone with autism, or for that matter adhd. In a typical kindergarten classroom, there is a teacher talking, other students doing things, and perhaps he just doesn't know how to pick what to focus on.
Do the parents have any other parents of kids with similar issues they can talk to? Sometimes that is very helpful, since maybe they will have some ideas to help through this rough time, or at least they won't feel so alone.
Other than just sympathizing, I suggest reading up on the disorders, and don't give up.