Can the guidance of my brother, who has started to pray and study the religion, be a result of my supplications for him, and does the Hadith: "For Allah to guide a single man through you is better for you than red camels," apply to me?

Allah is Generous and has promised to answer those who supplicate to Him. Therefore, it is probable that your supplications will have an effect on your brother's guidance, but this cannot be asserted with certainty. Be keen on guiding him using legitimate means such as advising him, having him listen to influential tapes, and finding good company for him.