Praise be to Allah.
Your desire to form another family is halaal, and your goal of having more children is perfectly legitimate. Your wife does not have the right to object to that. If she will leave you if you marry another woman, then she is a sinner. Help her to bear with patience what Allaah has decreed for her, and tell her that you will be fair and just as Allaah has commanded if you marry another woman. Break though the barrier of fear and look for a loving, fertile, religious woman, and pray Istikhaarah when you decide to go ahead. Put your trust in Allaah, for whoever puts his trust in Allaah, Allaah will be Sufficient for him. Be optimistic that Allaah will relieve your distress and grant you ease after difficulty. Keep calling the other son to Islam; may Allaah open his heart and guide him at your hands. We ask Allaah to give you strength.