Can my brother sponsor his wife using my tax information for a green card?

When a U.S. citizen sponsors a spouse in a marriage-based adjustment of status application, among the many requirements of the process the U.S. citizen must provide a signed Affidavit of Support. If that U.S. citizen does not have sufficient documentable income to meet the requirements, then it may be necessary to have a joint sponsor in the application process. Generally the joint sponsor may be any U.S. citizen or Permanent Resident who has sufficient documentable income and who is willing to assume the responsibilities contemplated in the Affidavit of Support (regardless of whether that person already may have sponsored his own spouse for immigration benefits). Perhaps this is what you meant by "using your tax information." Of course, the Affidavit of Support issues are among many others that need to be addressed in an adjustment of status application process. It would be wise for your brother and his wife to consult with an immigration attorney who, after learning all of the relevant information, could advise about eligibilities, options and strategies to attain immigration-related goals, and who then could offer legal representation in the often complex application process.