Hello,
very difficult. i agree that medication may be of help.
Also think your daughter should get assistance with how to handle him. There should a reward system for appropriate behaviour. Ie. he has to earn things he wants or likes with good behaviour. This will be tough to implement, but very important as he would get more difficult to handle as he get's older.
I have a 7 yr old son that has been diagnosed with Autisum and ODD. He started his ourburst around 5 he would kick and scream and was increasingly getting more violant. He scratched my face so bad I bleed he bit me reapeatly till he drew blood. I too hated the thought of medication, but my son's life depended on it. I called the dr and they started him on Risperdal and i seen a change in him almost immediatly. We had to adjust the amount to we found the correct dosage. He now is 7 and in 1st grade, he is still behind in school, however he is no longer hitting, throwing desks and being "mean", now he's hugging his teacher and being happy. Tell your daughter dont give in and medicine is not always the answer, however in can be the answer to helping your son and family.
Is your grandson seeing a psychologist or psychiatrist on a regular basis? I'm really at a loss as far as advice. I've read about violence in autistic children, but not this extreme or at such a young age. And not with something as high functioning as Aspergers. There could very well be something more going on here. I think if I were your daughter, I would take my son back to a psychologist/psychiatrist and demand that they do further testing. And I would consider medication. Good Luck.