I am Indian and work at Baoding in Hebei. I stay with my wife and son here.

We all 3 have China residence permit and I also have foreign expert certificate. I like to invite my wife's uncle & aunty to China and stay with us for 1 month. Which visa category can they come? Do I need to write about tourism also in the invitation? As per my information they don't fall in category of relatives mentioned for S2 type. Do we need to prove the relationship of uncle and aunty with wife?