You can petition for your parents now, but since they came in illegally, they have to return to their home country to attend their visa interviews. If they have been unlawfully present in the US for more than 1 year, they will also need to file for a discretionary waiver in order to return to the United States. To be eligible for the waiver, they must prove extreme hardship to a parent(s) (your grandparents) who has legal immigrant status in the US if their waiver application was not approved.
Answered on Oct 08th, 2013 at 10:24 AM