Oh man, that sounds hard. If the big hugs are not helping, I'd avoid them. Some people do better with something like that, and some get even worse. If you can get him isolated, in a quiet, dark room, sometimes that can help, as well. And, strange as it may sound, he may really not be hearing you when he's in a melt-down. When the sensory overload kicks in, it's often fight-or-flight for many. I know that, even though my melt-downs are quiet compared to some people, even when I'm "hearing" what people are telling me, I may not process it. Routines come in handy for this for me. What I do, is I build a routine of what to do if I feel something out of control. (I have to do this well in advance and practice it.) For your son, you might work with him after he's calmed down from an episode and ask him questions about what might have helped him most. Some suggestions on your part might help; any strong response for or against would be good indications. Then, ask him how he would like to learn things to make it a little easier for him. I'd be willing to bet he'd be game. Then, if you have a set way you plan to do things and signals you practice and ingrain, it may make calming down easier. As for the younger brother, if you give him strategies as a way of allowing him to help, too, I'll bet that would help, as well. I would imagine that he idolizes his older brother (no matter how much they fight, lol), so any way he can "help" would be very attractive to him. He would just have to be prepared to accept that, even if he does help, he might not always get the response he wants from his brother.

I'm sorry this got so long. I know that preparation for meltdowns can only help a little in some cases, but I have learned that any amount of control I can get, no matter how minimal, makes me less likely to completely panic and more likely to calm down in a reasonable amount of time. Any kind of feeling of control can help create some triumph and strength in that kind of adversity.