How to renew WORK VISA

I am working in China since last 2 years and now i have changed my job and my new employer is asking me to go back Pakistan to get new visa even my ex-empolyer's visa is still valid. I am living here with my family and my family visa is also sponsored by my ex-employer, I got all of my documents like " work permit, invitation letter, Medical and foreign office letter" which you required to give me new visa but i have a deep conceren that my family is also visiting back Pakistan so should they also need to apply new visa along with me or they can apply after the expiry of their previous visa. My family visa is still valid for September,2012.My new emplyer in china has said that my family shouldn't need to renew visa at this stage and their visa will be renew in china later in sept,2012 when it will expire so i just want to make it sure that what should i do , will you also cancel thier visa as well when you will cancel my ex-visa when i will apply in next month or you will just cancel mine and give me new visa? Please guide me that what should i do coz my family also want to fly back Pak but i don't want to apply their visa at this stage coz their visa is still valid, Plz guide me what should i do?