What is the ruling on giving an apartment from a building owned by a person to the children of his deceased brother?

What you have done by giving an apartment to your deceased brother's children is a good and rewarded deed. It is considered an act of maintaining kinship ties, which Allah has commanded, and it is hoped that Allah will expand your provision because of it, in fulfillment of the Prophet's (peace be upon him) saying: "Whoever wishes that his provision be expanded for him and his life span be extended, let him maintain his ties of kinship." And if they are poor, your charity to them is better and greater in reward, due to the Prophet's (peace be upon him) saying: "Charity given to a poor person is charity, and to a relative, it is two: charity and maintaining kinship ties."