请教老师I-131

我给父母申请绿卡，打算同时递交I-131. 请问以下几个问题

1. Part 2 Application Type： Should I check '1d I am applying for an Advance Parole Document to allow me to return to the United States after temporary foreign travel‘？ 

2. Part 4 1a purpose of trip: Can I simply put 'visit family members in China'? Or should I provide more details. Do I need to provide documents of proof for this purpose?

3. Part 7 On a separate sheet of paper, explain how you qualify for an Advance Parole Document, and what circumstances warrant issuance of an Advance Parole
What should I do? Do I need to attach a separate paper? And what reasons should I provide? I apply for I-131 for my parents to go back to China in case their Green Card will not be approved within 3 months as they plan to go back to take care of my grandfather for a couple of months.

Thank you very much!