Is it permissible to delay giving zakaah until the rent is due from the poor person so that it may be paid with zakaah?
It is not permissible to delay paying zakaah from the time when it becomes due for the one for whom it is obligatory, as we have explained in the answer to question no. 67578. What you have mentioned is not an excuse for delaying it when there are so many people who are entitled to it in Muslim countries.
If you think that these families are more deserving than others of receiving your zakaah, then there is nothing wrong with you giving the rent before it becomes due, if you think it most likely that they will be staying in the same house or, if they move, they will not lose the money. Giving it ahead of time may be a cause of reducing some of the rent for them.
It is also possible to pay some of the zakaah for the coming year in advance in the month of Muharram, and to pay the rent that is due on time, from the zakaah on your wealth. Then you can subtract what you already paid from next year’s zakaah. See the answer to question no. 98528
You can also pay the rent on these families’ homes directly to the landlord, because when the rent becomes due, the renter is then in debt; in that case it is permissible to give the money directly to the one to whom the debt is owed. See the answer to question no. 46209.
And Allah knows best.