2. your parents need to explain to the VO why they extended the status last time and they need to have good reason for this vist. My mother stayed here for 364 days last year, and she got the visa after 1 year this time.
3. You can submit N-400 up to 90 days before you meet 5-year requirement.
4. depends on your local CIS office. In bay area it takes 6-8 months for interview. It usually takes longer time for consular processing because you have to go through I-130, fee bill, packet 3,interview schedule, background check before they can finally enter the U.S.
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