How joint rights devolve?

This is quite a different situation from what we discussed earlier. Here a single person makes a promise to two or more persons jointly. The promisor is single person and promisees are more than one. All the joint promisees during their lifetime, on death of any of them, the legal heirs/representative of the deceased promisee become promisee with other surviving promisees and on death of the last surviving promisee the representatives of all promisees jointly acquire rights to enforce the contract.