You can file an I-130 petition for each parent right away. Both will get their green cards at the same time and either one can then file a petition for your minor sibling. The sibling if a minor will get the green card within 3 years. Pending approval of the siblings' green card, each parent can take turns in visiting the sibling in Mexico since as legal residents they can travel as many times as they deem necessary.
Answered on Mar 18th, 2013 at 9:03 PM