Is the contract formulation that stipulates the sale of a plot of land to the son, along with exempting him and his children from the remaining amount should the father pass away before the full amount is collected, and that the remaining amount be paid as sponsorship for orphans as a charity on behalf of the father should the son pass away before him, Islamically lawful or not? And what is the correct formulation if it is not lawful?

Selling the land for the mentioned price is valid as long as it represents its value without undue favoritism. The conditions related to the death of the father or son are valid; thus, exempting the son and his heirs from the remaining price if the son dies before his father is permissible, and it is a conditional discharge. As for the father's condition that the remaining installments be paid as charity on his behalf for the sponsorship of orphans if he dies first, this is a valid will that is executed if it is within one-third or less. If it exceeds one-third, the excess depends on the heirs' consent.