What is the way to deal with the eldest brother's rejection of a non-Saudi suitor, and his threat to kill and harm him, despite the father's approval and the desire of both parties to marry?

It has been previously stated that a guardian should not reject a suitable suitor who possesses religiosity and good character.

The decision regarding this marriage rests with you and your father. Try to convince him and involve people who hold influence with him to reprimand your brother.

If your father is convinced, then praise be to Allah. If he insists on refusing without a legitimate religious reason, then you have the right to refer the matter to the Sharia (definition) court, or its equivalent. If the coercion is proven, they will arrange your marriage.

However, if you prioritize filial piety towards your father and choose to forgo this young man and seek someone else, it would be better. This is because a girl’s marriage without her family's approval might lead to her isolation and their estrangement from her, thus preventing her from enjoying the marriage.

We do not advise informing your family about your brother's threat to the suitor's family, as the harm from doing so might outweigh the benefit. Similarly, reporting the matter to the police might not serve any benefit and could complicate matters further, unless you fear that he will carry out his threat and cause you harm, in which case you may do what protects you from him.