You can stop looking at pornographic pictures if you lower your gaze as it purifies the heart and soul and actions, and it prevents the poisoned arrows from reaching you, for a look is one of the poisoned arrows of Iblis.

If they had both repented to Allah before getting married, and they regretted the haram things that they had done, then their marriage is valid. But if they did the marriage contract before they repented, then the marriage is not valid and they have to repent to Allah and regret what they have done, and resolve not to do such a thing again, then they should make a new marriage contract.