Can I fix my parents papers at 21 being married?

A U.S. citizen age 21 or older generally may petition for parents to adjust status to become Lawful Permanent Residents (to get "Green Cards"), regardless of whether the U.S. citizen is married. If she is married, then the amount of documentable income necessary to meet the Affidavit of Support requirements will need to take the spouse into consideration when calculating the family size and amount of needed income - if her documentable income is insufficient, a joint sponsor may be needed. There are many other details that would determine eligibility for the Adjustment of Status application process. It would be wise for you and your parents to consult with an immigration attorney who, after learning all of the relevant information, could advise about immigration-related eligibilities, options and strategies and could offer legal representation for the application process (which often is significantly more complex than it may first appear).