B2 dropbox qualification

[vanv]

Hello,

I have multiple questions regarding B2 visa.

1) Are dropboxes open for B2 visa currently in India-Chennai? How long is the waiting time?

2) I am trying to figure out if my parents are eligible for B2 dropbox.
both visa and I-94 is expiring on Feb 2nd. We have applied for extension thinking they might need to stay longer than Feb 2nd. I haven't heard from uscis yet. They might travel back to India before Feb 2nd. Would she be still eligible for dropbox when there is a pending I-539 petition here?

3) Should they travel before feb 2nd to be eligible for dropbox?

3) Should b2 visa holders stay in home country for 6 months before traveling again to US?

4) I heard b2 visa interviews are only for emergency. what situations are considered as emergency? We are having a baby in June. Thats' the reason I am trying her to be here.