How to renew H4 visa before H4 visa extension approval notice get expiry+ also H1 spouse changed the employer

I went through many forum threads published here; but couldn’t have a proper solution for my situation. My situation is briefed below.

I got H1 visa (Employer A) in 2013 Nov and came to US in Dec 2013. My wife came to US as my dependent (H4) visa in Mar 2014. My H1 visa validity was till 2014 Oct. I applied extension for my H1 visa and my wife’s H4 visa in Jul 2014 itself through my employer immigration team. But lack of some documents, my visa extension petition fell to RFE and we got that status change in Aug 2014. We submitted the additional documents (to clear RFE) in Aug 2014 last week. Meanwhile in Sep 2014 second week, my wife went back to India for delivery. My H1 visa extension got approved for another one year (Till Sep 30 2015), also I received the approval notice for wife’s H4 extension (Till Sep 30 2015).

When I went to India in March 2015, I used the drop box facility and received the new extended visa (H1) in my passport. Based on that, I alone came back to US.

In May 2015, I have changed my employer (Employer B). “Visa transfer petition (I-129)” received in USCIS on 26 May. I got the petition number and started in Employer B job.

USCIS website showing, my I-129 approval will take 2 months period (I am expecting that in 2015 July last week).

I am planning to bring my wife and kid to US in last week of Aug 2015. For that, my wife needs to get the new H4 visa (based on the extension approval notice) and my kid need to get new visa.

My questions are given below. Our preference is to avoid appearing for visa interview travel, as it is hectic to travel with a 3 month old baby.

  1. Whether my wife needs to go for visa interview since I have changed the employer? Or she can avail the interview waiver drop box facility because she have H4 extension approval notice, but based on my previous employer (A) petition?. H4 visa extension is valid till Sep 2015

  2. If she is eligible for interview waiver drop box facility, what is the petition she need to keep in the drop box envelop (My employer B I-129 approved copy OR her visa extension approval copy from employer A OR Both those documents?)

  3. If my employer B I-129 approval getting delayed, whether she can avail the drop-box facility with Employer A H4 extension approval notice + my current H1 visa (employer A)? Since the expiry of that H4 extension approval notice is 2015 Sep 30, USCIS will provide a new visa which will have only one month validity?