After 25 years of being involved with representing people, I have learned that there are two sides to every story. Nevertheless, to answer your question:
1. Have Dad and Mom execute a letter to the lawyer sent certified and tell him to stop working on the file immediately. Then tell him a new lawyer will be taking over the file. Then go get a new lawyer.
IF everything you said is true, you might be able to file a grievence against him. YOu could have both mom and dad give you a limited power of attorney, which would allow you to act on their behalf as to the lawsuit. Then the lawyer would have to respond to your questions.
I can only answer this question from the perspective of Texas Law and it may or may not have application in Georgia, and based only on the facts as you presented them ( probably no recording was made of the conversation). To answer you questions: First, an abusive or disruptive or angry attorney is not acting in an ethical manner; so the behaviour is not ethical. Second, such behaviour is not an excuse for an attorney to fail to communicate with you. It is unethical for him not to answer you in a manner that insures you will understand. Third, in Texas if you terminate an attorney without cause, he can still maintain an interest in your case, and another attorney may not be interested in taking your case if the previous attorney is still claiming a 1/3 or more interest. Thus, if the attorney continues to improperly discharge his responsibilities to you and your family, you need to ask him to withdraw and relinquish any interest he has in your family's file. His failure to do so may become the subject of a grievance and you should consult with an attorney in Georgia about filing a complaint with the Georgia Bar Association.