On the applicated for the Disability tax credit (DTC) there is a question that asks which supporting family member the applicant would like to transfer the amount to. If you are listed as the supporting family member on your brother's application, then he can transfer his disability tax credit to you.
If you are not listed there on your brother's form, then he will not be able to transfer his credit to you. You can change this by submitting a written request to the CRA.