Is this commercial transaction permissible in Islamic law, where a brother buys goods from their source, then sells them to his brother so that he (the first brother) profits first, and then the second brother sells them for a two-dollar commission to the final buyer, knowing that the second brother could have bought the goods directly from the source?

A merchant must be truthful in his trade to attain blessing, as stated in the Prophet's Hadith: "If they are truthful and make clear, they will be blessed in their transaction. If they conceal and lie, the blessing of their transaction will be effaced."

The agreement between your brother and the buyer has two possibilities:

1. Your brother is an agent for the buyer: In this case, the agent must act in the best interest of his principal. It is not permissible for him to favor you at the expense of the buyer, as this is considered treachery, a point affirmed by Shaykh al-Islam Ibn Taymiyyah and Shaykh Ibn Uthaymeen. This ruling also applies to brokers. 2. Your brother is a seller and set his profit at two dollars: This sale is not permissible and is invalid according to the majority of scholars due to the unknown price. Some scholars permit it by making the price the customary market value. Even if its validity is affirmed, the seller must be truthful and trustworthy, and refrain from deception. Increasing the profit through deceit is a deception of the buyer and an unlawful consumption of wealth.