The Gemara (???? ?”?) says that two of them were due to their brother becoming tamei (on two separate occasions).
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???? ?? ????? ????? ???? ???? ???? ????? ????? ??? ??? ????? ?????? ???? ??? ???? ???? ???? ?? ??? ?????? ?? ????? ??? ??? ??? ????? ?? ???? ??? ???? ????? ?????? ???? ?? ????? ????? ???? (??) ???? ???? ????? ????? ??? ??? ????? ?????? ???? ??? ?”? ???? ???? ??? ?? ?????? ????? ???? ?????? ????? ???? ?? ????? ?? ???? ????? ??? ???? ??? ???? ?? ??? ????? ???? ???? ???? ???? ?? ???? ??? ?? ??? ??????