How can a son get married and fortify himself, while remaining in his parents' home and supporting them financially, without falling into disobedience to Allah?

If marriage conflicts with supporting one's parents, and the person is capable of bearing the costs of marriage and fears falling into zina (unlawful sexual relations), then marriage is obligatory and takes precedence over spending on parents. This is because it is part of one's own necessary expenses, and similarly, the wife's expenses take precedence. The Prophet, peace be upon him, said: "Start with yourself and give charity to yourself. If there is anything left, then for your family. If there is anything left from your family, then for your relatives..." Spending on parents is not obligatory for the child unless they are poor and he is rich. It is advisable to inform the parents of the true situation and your need for marriage, and to seek assistance from someone they trust to convince them, along with supplicating for matters to be eased.