i want to go china for phd and want to take family with me (wife,two kids, mother). what required?

In your situation, you need to apply for X type. It doesn't require bank statement for you. You should apply for X type first and then ask your university to send invitation letter to your families for applying S type. In order to apply for X type, you should submit the following documents apart from your passport, application form and a recent passport photo.
1. admission letter from Chinese university (original and copy versions)
2. JW202/201 form (original and copy versions)
3. your diploma authenticated by your Ministry of Foreign Affairs
4. health certificate. You can have it done at these two hospitals without getting the result authenticated by your Ministry of Foreign Affairs

KRL Hospital
Aiwan-e-Sanat-o-Tijarat Road, G-9/1, Islamabad
Tel# 051-9106278
Fax# 051-9106285

Chinese Acupuncture Centre
No 3, 4 First Floor Near Bank of Punjab Rajan Plaza, F-10 Markaz Islamabad
Tel# 051-2291764, 210-3449

For families, they should apply for S type, it requires the following documents excluding their passports, application forms and recent passport photos:
1. invitation letter from duly authorized unit or your university
2. invitation letter sent from you
3. copies of your passport and resident permit
4. kinship certificates (marriage certificate, your kids' birth certificates and certificate that proves your relationship with your parents). You should have these certificates certified by your Ministry of Foreign Affairs. If possible, get several copies because you need them to change your X and your familie's S types into temporary resident permits.
5. health certificate

Pakistanis are exempted from the fees. It takes four working days to deal with your applications.