Is it permissible to keep one electricity meter supplying the parents' house and the married son's apartment in order to benefit from the employee discount offered to the parents?

It is not permissible to do so except with the permission of the employer, because it is a form of deception and trickery. The employee is obligated to abide by the contract and its conditions, based on the words of Allah Almighty: "O you who have believed, fulfill [all] contracts," and the words of the Prophet, peace and blessings be upon him: "Muslims are bound by their conditions," and his saying: "The wealth of a Muslim person is not lawful unless given willingly by himself."