Will the mother and daughters be held accountable before Allah on the Day of Judgment for the father's viewing of forbidden things?

The fundamental principle in Islamic law is that no one bears the sin of another, as confirmed by Allah’s saying: "And every soul earns not [ill] except against itself, and no bearer of burdens will bear the burden of another." However, Islamic law has made it obligatory to enjoin good and forbid evil to the best of one’s ability. If a Muslim fulfills this, then the misguidance of others will not harm him.

Therefore, if you do what you can to rebuke your father for watching forbidden things, his persistence will not harm you. You must continue to advise him with wisdom and gentleness, encourage him to attend religious gatherings and associate with righteous people, play beneficial audio recordings for him, and seek the help of some righteous individuals to advise him, without neglecting to honor and be kind to him. Your mother should also not neglect his rights and should be a good wife to him, while persistently supplicating for his guidance.