Get sister here

My parents got immigrant visa (IR5).I have 20 years old sister (DOB- July 27, 1995).She was here 3 years ago. She is in Nepal now and still holding valid B1B2 visa. Can she come here and my parents file I130 and I485 together? Do both of my parents have to come here to file I130 or either one of them can file her I130? How long do they have to wait to file after they come here at United States?

I filed I130 petition for my sister. The priority date is August 2012. Can we file separate petition? What are my better options to bring my sister here legally in United States?

Thank you for your time and your help will be greatly appreciated.
Sunny

Get sister here