My parents are divorced. Can I petition for my mum, dad and step mum. If now what options are available to my step mum to come to USA

As you know, you can apply for your mom and dad (I will assume that you were not adopted by someone else and that these are your natural parents). For your stepmother, you can apply directly for her as long as your father married your stepmother before you turned the age of 18. If not, you can petition for your father, and he can then petition for your stepmother when he becomes a permanent resident. Due to the limitations of the Lawyers.com Forums, Alan Lee & Arthur Lee, Esqs.’ (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.