Should the mother be informed about the discovery of pornographic films and indecent conversations on the father's computer, or should this matter be concealed?

It is not permissible to spy on your father by prying into his private matters, as it is forbidden, according to the Almighty’s saying: "And do not spy." However, since you have become aware of a reprehensible act your father is committing, you must advise him and remind him of the impermissibility of his action and of meeting his Lord. You must conceal his secret and not expose him. If he persists in his action after being advised, you may inform someone who has influence over him, such as his brothers or friends, or your mother if she is capable of preventing him and you are secure from any corruption arising. And you must supplicate for his righteousness.