S1 or S2 Visa for family

Dear Sir
I am applying for Z type where in I have got employment certificate & invitation letter from my future company in China. However they have not mentioned my family members name in invitation letter. Generally they do not do so. They are asking me to bring my family along with me on S1 or S2 type. I should apply their S type at the same time when I apply for Z type for me. Is it really possible to get S without any invitation letter? Could you please suggest the way out.