Should I wait or leave the young man, given his mother's rejection of our marriage due to his father's will, and would my marriage to him with the approval of his paternal uncles and maternal uncle, without his mother's consent, be considered an act of disobedience?

The mother is not permitted to prevent her son from marrying someone he desires, unless she has a valid, recognized শরعي (shar'i) justification. The deceased father's refusal is not a binding وصية (wasiya - will/injunction). Marriage without the parents' permission is valid. However, honoring one's parents is obligatory, so the young man is advised to try to persuade and appease his mother. If she insists on refusing, he should forgo the marriage unless he fears falling into haram (forbidden acts) or suffering significant harm. Neither the father nor anyone else has the right to prevent a mature man from marrying whom he desires, but he should seek to appease his mother after the marriage. One is warned against love and infatuation relationships between men and women before marriage.