What is the ruling on increasing the amount when selling a partner's share in installments, and what is the ruling on a merchant selling a car to a third party after purchasing it from two partners, taking a down payment and a profit in installments?

The aforementioned transaction is Islamically forbidden as it encompasses two prohibitions: The first is a sale with a condition, and the second is an agreement that the seller will repurchase the same item for more than its price on credit (debt), which leads to usury (riba). However, the suggestion of the partner with twenty (shares/units) to his partner with ten (shares/units) that he buy his share from him on credit for fifteen is permissible.