My mother is uneducated and she doesn't know her age i mean when she was born, and my brother wants to petition for her we are confused

Your mother and other relatives should discuss her date of birth and try to establish what it is before your brother petitions for her. Ultimately she will have to present proof of birth in order to immigrate. As long as she still has to do that, she should try to get that step out of the way at the beginning. Even without documents, a certificate from the municipality that she claims to have been born in stating the reason why there is no birth certificate and two affidavits of birth in lieu of birth certificate by persons who know the facts of her birth might overcome the hurdle of lack of documents. Due to the limitations of the Lawyers.com Forums, Alan Lee, Esq.'s (the "Firm") participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting a question. No Attorney/Client relationship is or shall be construed to be created hereby. The information provided herein by the Firm is general, and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice nor as the basis for making any decisions of legal consequence.