Does the mother's divorce take effect if the son proposes before graduation, given that the father swore an oath of divorce regarding this, and is not yet aware of it? And what should the son do in this situation?

The majority of jurists hold that a conditional divorce takes effect as soon as the condition is met. However, Sheikh al-Islam Ibn Taymiyyah details the conditoner's intention: if he intended to threaten, then the divorce does not occur, and he owes an expiation for breaking an oath. But if he intended to cause the divorce, it takes effect upon the fulfillment of the condition.

Accordingly, if the father did not qualify the divorce with his knowledge of the engagement, then it takes effect according to the majority of jurists. It does not take effect according to the second opinion if he did not intend divorce. If the divorce occurred and the father had intercourse with his wife during her iddah (waiting period), this is considered a revocation of the divorce by some scholars, as mentioned by Ibn Qudamah in "Al-Mughni." However, if the father conditioned the occurrence of the divorce upon his knowledge, then the divorce does not take effect until he gains that knowledge. The son must repent and seek forgiveness for disobeying his father.