Is Zakat due on income from property and restaurant rentals, in addition to money held in current and investment accounts that has been designated for three Ramadans, knowing that the money is income from a job and rentals?

Zakat (definition) is obligatory on money obtained from rentals if a year has passed and the money has reached the aformentioned nisab (definition). You have the choice between paying zakat on each installment when its year is complete or paying zakat on all your money at once. The second option is more beneficial for the poor, and it is Islamically permissible to pay zakat on some of the money in advance.