extending S2 visa in Zhejiang

Greetings, my sister and her hubby came to visit me on S2 type (4 months) now it has been almost 3 months, I am living in Guizhou province, but recently they went to Hangzhou and Zhejiang for travel, now they want to extend their S2 and stay more and explore China and see other places, my question is, the PSB here in Guizhou told me that they can renew it (extend it) from other provinces and no need for them to come back here, is it possible they renew it in Zhejiang province? and what do they need to(i.e passport, pics, what are the requirements)? and where to go? local PSB in Zhejiang which place is better or quicker. thanks a lot for helping and answering