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By law the landlord is permitted to require all adults to be put on the lease and thus require a background/credit check. I am sorry I wish I had better news. The new manager is completely within their rights to require this prior to renewing the lease for any more time. They can approve the lease for you but require him to leave if he is not able to pass the credit check.
I am sorry, I wish you and your brother the best in the new year.