Is there any Sharia doubt about the legitimacy of including a nephew as a partner in a shop rented under an old lease agreement, given that the lessor receives a monthly sum from the profits, and does the owner of the rented shop have the right to intervene in this partnership?

The Fatwa's Summary: The duration must be specified in the leasing of houses and shops. A contract that does not specify the duration is jurisprudentially invalid (fasid) and it is not permissible to rely on a law that validates it. As for partnership (sharika), it is permissible for the capital therein to be goods valued in cash at the time of the contract, and the profit shall be shared between the partners according to their agreement, provided that each partner's share is a common proportion of the profit, not a fixed amount.