Assalamu alaikum. My brother is my wali but is mentally ill and often unable to make sound decisions. My stepfather raised me and I call him Dad. Can my stepfather be my wali instead? JazakAllahu khayran.

Imam Ibn Baz (may Allah have mercy on him) said: The obligation is that the guardianship in marriage (Nikah) should be assumed by the closest [male relative], followed by the next closest. This is the most correct opinion among the scholars; it is undertaken by the closest, then the next closest. The closest is the father, followed by the grandfather, then the sons, then the full brothers, then the paternal half-brothers, and then those who come after them—such as the son of the full brother, the son of the paternal half-brother, the full paternal uncle, and the paternal half-uncle—just as in the order of inheritance.