What is the legal ruling for someone who was afflicted with zina (unlawful sexual intercourse) and violated another's honor, then repented, married, and had children, and years later married the woman whose honor he had violated after learning she had not married, while the first wife insists on the divorce of the second wife?

You are not obligated to obey your first wife in divorcing your second wife. You can try to convince and appease her. If she insists on her opinion, you are not required to obey her. If you fear problems, then consider your matter carefully and seek Allah's guidance through Istikhara. Be keen on marrying a righteous woman, and stay away from an adulteress unless she repents. The more correct view is that you are not obligated to separate from her after marriage, and you should strive to guide her. One who repents from a sin is like one who has no sin.