What is the ruling on giving zakat al-mal to one's brother if he is unemployed and owns a one-room house and only 5,000 riyals?

Scholars have differed on the definition of wealth that precludes receiving zakat. The predominant view is that whoever possesses what suffices for their basic needs is considered wealthy and is not eligible for zakat. If the aforementioned amount is sufficient for your brother, then he is wealthy. Otherwise, he is poor, and zakat is permissible for him. Giving it to him would be preferable, as it is both charity (sadaqah) and maintaining kin ties (silah), provided that his expenditure is not obligatory upon you.