Is the owner of a device sinful if his brother puts pornographic pictures and videos on it, with his knowledge and his attempt to prevent him?

Reprehensible clips and images must be denounced and removed when one has the ability to do so. If you are able to prevent their publication and you do not, then you are sinful. If you are unable to prevent their publication but can remove them after they have been posted, then you are obligated to do so, otherwise you would be sinful, especially if the device belongs to you, because the Prophet, peace and blessings be upon him, said: "Whoever among you sees an evil, let him change it with his hand; if he is unable, then with his tongue; if he is unable, then with his heart, and that is the weakest of faith." Reporting them to have them blocked is a form of cooperation in righteousness and piety, as Allah Almighty says: "And cooperate in righteousness and piety."