S.H.
Your son is needing to "grieve."
In a young child, they dont' know how to do this...thus they act out.
Just don't punish him for it... he NEEDS to grieve, and needs to just be.
Grieving can take time... don't put a "deadline" on it.
If he needs extra help, perhaps a support group or a counselor can help.
This is difficult time for an adult, much less a young child.
They need to "know" coping skills, and that it is okay to cry, or feel angry... this is all a normal and natural response to grieving.
Also, with boys especially, they MUST know that it is okay to communicate, to express themselves, to even cry. It's not good to teach them to just be "tough" about it or life's difficulties.
For him at this time of "stress" and even loneliness... he is even probably feeling like NO ONE understands him or what HE is going through.
Just offer him lots of comfort, allow him room to feel and to be moody... and to feel sad... and be a soft place for him to fall. If he cannot adjust to the loss of his uncle... then counseling might be a great thing for him. But don't "rush" it... everyone has a different time-line in how long they take to get over something like this.
Your son's life has changed, he lost someone he was very close to, their shared love of computer games and activities is now gone, and his best "buddy" is no longer here. Your son probably has a big empty place inside of him now. It's very hard.
Perhaps, let your son go to his uncle's grave... and take flowers for him every week even, if this makes him feel better. Then when he is at his grave, let your son have some solitude, step back, and let your son "talk" to his Uncle in private at his grave. This may be a helpful thing for him...
Your son, will need "closure" a part of his grieving process too. In time.
All the best,
Susan