Is silence about discovering a breach in the barrier that prevents access to pornographic websites, which the parents still believe to be effective, considered a lie? What is the necessary action to solve the problem, and what is the legal ruling on this silence?

If your parents prevent access to pornographic websites, then alert them that the barrier does not entirely prevent it, especially if you know that someone is using the device to access those websites. You must alert them, based on the saying of the Prophet, peace and blessings be upon him: "Whoever among you sees an evil, let him change it with his hand; if he cannot, then with his tongue; if he cannot, then with his heart—and that is the weakest of faith."