1. How sound is the Hadith that states the Prophet, peace be upon him, said: "If two Jews meet, they conspire to kill a Muslim"? 2. Is it permissible for my friend to seek help from another male relative to propose to a girl if his father refuses to attend and the girl's father insists on the guardian's presence?

There is no hadith with the wording mentioned in the first question. As for the second question, obedience to parents in what is good and permissible is obligatory. It is not considered good and permissible for a father to prevent his son from marrying on the pretext of his young age. Therefore, the son is permitted to marry without his father's approval, and this is not considered an act of disobedience. However, it is not permissible to lie by bringing another person as a guardian. The best approach is to try to persuade the father through supplication and seeking help from wise individuals to influence him.