I am on H1B visa. I entered USA along with family (wife and 2 kids) in March 2008, and we all got I-94 with validity till October, 2010. All are with me in USA now.

In November 2009, I changed employment and got my I-797 with attached I-94 which is valid till October 2012. Now, I want to file I-539 (Extension of Status) for my wife and kids:

Wife - 40Yrs
Daugther - 18Yrs
Son - 5yrs

1. My wife will be filing form I-539.The instructions for I-539 says Unmarried children under 21yrs of age can be included as co-applicants. The fee for filing is given as $300. Here I am getting confused - is this fee for all applicants on the form, or per person?
2. Is it ok to include my children on the same form with my wife? Will they get separate approvals?
2. Can I do e-filing of I-539?