None of them can by any means redeem his brother. The text is suspected. If we read אַךְfor אָה, with Ewald and Professor Cheyne, the right translation will be, Nevertheless, no man can by any means redeem himself.
With all his boasting, the rich man cannot effect his own redemption; nor, however great his wealth, can he give to God a ransom for him; i.e. for himself. "Brother" is not used in the Psalms in the sense of "fellow-man," but only in the literal sense of close blood, relation (Psalms 35:14; Psalms 50:20).