I have a 17 year old step son that wants to come visit us in the us. He is in Mexico

Sorry, not likely to be successful.  You could sponsor him for permanent residence, as his US citizen step-parent, but of course you have issues relating to his mother's best interests.  Whenever she is willing to allow him to leave home, you could begin a case.  If you start it at least 12 months before his 21st birthday, there's a good chance the process could be complete within 12 months.  Good luck.