Is it permissible to count the money lent to two people for building their homes as Zakat on wealth when the Zakat is due, knowing that the intention was made for this at the time the money was handed over, and without informing the debtors beforehand, then informing them later of their exemption from the debt at the time of paying Zakat?

Zakat is only paid to those who are eligible to receive it. What was paid to the two brothers can be considered zakat if the one paying it intended it as such, and if they were among those eligible to receive zakat. As for paying zakat for building a house, if the builder is able to rent, it is not permissible for him to take zakat for that purpose. However, if he is unable, he is given what suffices him for housing for one year, according to the majority of scholars. The Shafi'is hold the view that it is permissible to give to the poor to buy a dwelling if they do not have a dwelling that suffices them and their dependents, and they are unable to secure housing, even by renting.