What are the consequences of dissolving this partnership, and what are the best ways to dissolve it? Am I entitled to complete the project on my own, or to divide the clients I have acquired? Or is it better to abandon the project entirely? Is his action of spreading the word that he is the one deserving of credit correct? And what kind of partnership is this?

The agreement between the two brothers – if the questioner's work is limited to selling goods – is not a partnership, but rather he is an employee or an agent for a wage, with a percentage of the profit. The validity of such a lease is disputed: Imam Ahmad considers it valid, while the majority of scholars do not, and they hold that all profit belongs to the owner of the goods, and the worker is entitled to a fair wage (ujrat al-mithl).

The transaction could also be construed as mudarabah bi al-'urud (profit-sharing in non-monetary assets), which is also a matter of dispute: the majority of scholars do not consider it valid. Those who do, stipulate that the value of the assets at the time of the contract must be the capital, which has not occurred here.

Some early scholars, such as Ibn Abbas and Ibn Sirin, permitted a brokerage fee that exceeds a certain price. However, the majority of scholars do not permit it because it is an unknown wage or involves gharar (uncertainty), whereas Ahmad and Ishaq permitted it by analogy with qirad (profit-sharing partnership).

Malik does not permit qirad except with al-'ayn (gold and silver), and does not permit it with al-'urud (non-monetary assets). This is also the view of al-Layth, al-Thawri, al-Shafi'i, and Abu Hanifa. However, Ibn Abi Layla permitted it with al-'urud.

If the transaction is ruled invalid, then the money and its profit or loss belong to the owner of the goods, and the worker is entitled to a fair wage (ujrat al-mithl).

As for completing the project and taking customers, there is no harm in it in principle. However, avoiding it to preserve the brotherly bond is a righteous deed, and an agreement to divide the workplaces and customers is better for them both.

Attributing favor to oneself is bad character and ignorance; for all favor belongs to Allah, the Provider, the Generous.