My parents came to US this May with B2 visa (expiration date: March 2013). I filed I-130 with their I-485 petitions for their green card application this August. The biometrics service was done in September. However, no information about interview was received yet. Due to my grandma's illness, they need to go back to China. My questions are:
1. Can they use current B2 visa to re-entry US for interview this December or early next year depending on the interview appointment schedule? or
2. Do they need to apply for AP?
3. If AP is required, do they have to receive AP before they leave US, or I can send AP to them after they go back to China?
Thanks very much in advance!