What is the ruling of Islamic law regarding a dispute between two brothers concerning the payment of one brother's share of land and buildings, after one of the brothers reneged on a joint construction agreement and wished to reclaim what he had paid and the value of his share, and then the other brother delayed in making the payment?

If the contract between you was made on the basis that payment would be made within six years without specified installments, then your brother does not have the right to annul the contract for non-payment as long as the term remains; because the term is a right of the debtor and binding on the creditor if it was part of the contract. However, if the contract was made with specified installments, then your brother has the right to demand what is due from them, and it is not permissible for you to delay payment if you are able. In case of dispute, the matter should be referred to the Sharia court or to mutually agreed-upon arbitrators.