Hello, I'd like to help you with your question.
It is a great idea to have your son see a therapist for an evaluation. A psychologist or a Master's Level therapist would both be qualified to provide your son with an evaluation. Psychiatrists can as well, if you feel that medication is a priority. Psychiatrists will see people for therapy, but their focus is usually medication.
To find a therapist, talk with your son's doctor for a referral. Or you can search on line at http://therapists.psychologytoday.com/rms/. This link may also help:
Any therapist is going to welcome your input about what is going on with your son. When you make the appointment, let the therapist know about what you have been seeing with your son. Describe the problem, history, and the current symptoms he has. Also, if he is on any medications make a list. The therapist may also want to talk with you during the assessment for additional information.
If your son decides not to follow through, it is a good idea to talk with him as a family. But because of his anger issues, you may want to include someone who is neutral, like a counselor or pastor. Your son may feel he is getting ganged up on and become even more angry, making it too difficult to help him.
Letting him decline himself is ok too. It just will be hard on you and the rest of the family to cope with. If you feel you would rather take this route, be sure to consider therapy for the family so you have support and can learn of ways to cope.
If you need further guidance on finding a therapist, let me know.
I hope this has helped you,