Sorry to hear of your son's problems. I hope you don't mind my input. I used to work as a Psychologist and with children having emotional problems, but am by no means an expert. I agree you should get a second opinion. Also you may want to consider that if your son was very close to his granfatther he may be reacting to ongoing grief. Alongside that at his age he is likely starting the hormonal changes of puberty. He has a lot to deal with. Just letting him sort himself out may not be enough. There are trained counsellors who may be able to advise you, either through his school or your doctor. I am not suggesting you insist on him getting help if he resists, this will not achieve any good result, but he needs to have the right person to turn to. At his age he may be reaching a point where he feels less inclined to confide in his parents. You know how he has changed, better than your doctor, and if you are worried you should seek further advice. I hope things improve.
Thanks for your inquiry. I will be brief. I am not a child clinician, so I hesitate to comment on your child's condition. But based on the information you have provided, I would recommend that you seek out another consultation for your son. You have received assessments about your son that you and your family do not feel are accurate. I think that your question about how to help your son can apply to anyone who is seeking help from a psychologist or healthcare provider. In essence, if you don't feel confident in the accuracy of a provider's evaluation, you seek out a second opinion. Many people do this for medical issues, the same goes for emotional ones.