I did almost as behoove_me did, except I did not send Social Security card's copy and mortgage; instead I sent I-134. From my parents' side, they showed property papers, proof that they are my parents, a letter and employment documentation. Other than that they didn't even show bank statement. Because I didn't have much time, I scanned all the documents and sent them via email. It worked and they got visa. That was in January 2013. 

Hope that helps