B1/B2 Visa for my parents

[chandralekhak]

Hi 

   I have applied B1/B2 for my parent in Nov 2017 for my Graduation walk. They got rejected twice within 2 weeks of i had to resend them to interview because of grad walk .The income they provided was 550432 INR for my father(constructions, Sanitary works in public health engineering department and income from house property) and mothers(Business ,Saree sales) income for 3lakhs. They did not change 2nd time also, not sure why they rejected .They just gave 215 B form . I want to invite them know for my wedding and also have a sinus surgery. So can i ask the to explain both the reasons or just wedding. What are the documents needed for both cases for  them to carry .This time as i am on H1B visa can i sponsor them? Please help very urgent.