Rashed, two of ......... brothers attend primary school, wishes to be a school teacher after his graduation.

Explanation

"Whose" is right. The gap needs a possessive relative pronoun that links "brothers" back to Rashed: two of his brothers. "Them" would create a second main clause without a conjunction, and "which" or "whom" cannot show possession. So the clause reads "two of whose brothers attend primary school".