Is a young man's marriage to the one he loves, without his mother's consent—because she refuses his marriage before his older sisters' marriages—considered disobedience to her?

The young man's mother must fear Allah and help her son marry, and not be an obstacle to him from the Sunnah (definition) of the Messenger of Allah, peace and blessings be upon him. As for the questioner, she should not waste time waiting for the young man's mother's approval. If the mother prevents her son from marrying any woman, her obedience is not obligatory in that, because her prevention is not in what is good, and his marriage to her is not considered disobedience if the reason for the refusal is the marriage of his sisters. There is no religious impediment preventing the young man from marrying the questioner, and he must strive to satisfy his mother.