Changes of any kind can and often do effect a child's behavior. Sometimes they start acting out and others they become very insistent that others act or do things in a certain way/order.
So basically I am saying that the death of his grandfather could very well be a factor in his new behavior. It is normal to be angry and upset over the death of a loved one. Even as adults we don't often understand why we feel so angry when someone we love dies, I am positive that kids have difficulty dealing with their feels as well. My Nana passed away recently and I have felt myself feeling uncontrollably sad, irritated by small things that aren't really that big of a deal, upset about not being there for her.... the list goes on. I'm old enough and have been through this before so I recognize that the intensity of my feelings regarding unrelated things are part of what I'm feeling about losing someone I adored.
You and his parents have to have patience. It doesn't mean that you let him get away with unacceptable behaviors. It means that you are sympathetic, understanding, and help him find more appropriate ways to express his feelings. Maybe he needs someone to talk to about his lose. Maybe he needs to talk to his mom, his dad, his grandmother about how he feels. That someone might be another trusted adult in his life or a therapist at school or church or a doctor. Grief follows a pattern but it is cicular and individual so people progress through it at different rates.
Oh and one thing I was thinking is that living with his dad would mean that there isn't that daily reminder of his grandfather being gone.
the therapist and he told her she had not done anything wrong and my nephew was never abused by anyone. He admitted to lying and said the only reason he did it was to get his Mom and Dad's attention. She asked if it was anything to do with his grandpa passing and/or his aunt and the doctor told her he understood about them and that was not what was causing the change. He told her he was changing mentally and physically as most boys do and he needed a male figure to feel comfortable. My sister is single and had a boyfriend of 2 years but he wasn't there all the time and the doctor told her if she had been married he probably would have never done this. It was just a boy thing. They have decided to let him stay with his father for a little while and see how it goes. They are going to take it 1 week at a time and see if there is any change. They are not changing the divorce papers or making anything offical until they are sure it is what he wants and what is best for him. I think once he stays with his dad for a few weeks and sees he has other things to do and he will not get as much attention since his dad has a 2 yr old with his new wife things will go back to the way they were. I will keep you guys posted with any changes.