1.My employer is the same and the class of visa extension is also the same. Am I eligible for drop box ?
Yes if you have had the visa valid in past 12 months
2.My wife came with me on H4 and now has an extension approved for H4. Will she also qualify for drop box?
Yes if she had the visa valid in past 12 months
3.If we are both eligble for drop box, do we need to fill two DS 160 and take one single appointment. Where do we get to specify drop box option. Is it while scheduling the finger printing appointment ?
DS160 needs to filled by each applicant. When you pay fee and try to go to next step it will ask few questionnaire and then if you are eligible for dropbox, you will be notified and prompted a dropbox conformation letter