Should the delayed rent amount be delivered to the landlord's married children, knowing that their father is still alive and I do not know his house?

It is obligatory to pay the apartment rent to its owner. Charity or paying it to his children is not sufficient. Rather, it is obligatory to inquire about his address and deliver the money to him to clear one's responsibility. If direct delivery is not possible, it can be delivered indirectly, as mentioned by Sheikh Ibn 'Uthaymeen. It is also obligatory to advise the brothers about the necessity of returning rights related to others, because a sin related to the rights of people cannot be expiated by repentance alone, except by returning those rights, as explained by the Hadith of the Bankrupt. Therefore, one must hasten to return the money to its owner, and if finding his address takes time, a will must be written for the amount.