1. 我爸爸的姐姐还需要提供什么材料? (她是公民,不过已经退休长住内)
-Same as she did for I-130 filing.
2. 我爸爸现在B2 VISA 在美国,让他延期后留在美国办会不会更方便,还是最好回国去办?
-If he can extend his B-2 status until the priority date is current (排期到), then he can file I-485 within US. Thus, it is very convenient. Otherwise, if his status expires before 排期到, he has to leave US and apply for the immigration visa in China.
3. 他们B2 给到6/15/2015,priority date 是7/2/2002, 现在(March)F4排期是5/15/2002,有必要B2延期吗?
-Has better extend it in May if you find the priority date will not be current in June.
4. 2002年申请书上只有我爸爸的名字,排期到后可以让我妈妈和他一起办吗?
-Yes. If your mother is in US at that time, she can file I-485 together with your father. If she is in China, then she has to apply for the immigration visa in China (your father also had better apply for the immigration visa in China together in this case, thus you mother will get the immigration visa quickly).
5 . 费用大概是多少,如果爸爸妈妈一起办,需要请律师的必要吗?
-Up to you. It is very simple procedure if they are in US to file I-485. It is a little more procedure to apply for the immigration visa in China (not difficult).