My experience:
I do not think showing big bank balance or property guarantees visitor visa to the USA. Most important things are: family ties, interview, good application letter to consulate asking for granting visa to your parents or inlaws.
In my case, I asked my parents not to show anything else other than letter from my father's office. However, I asked him to take other documents with him if they ask you to show property or bank balance. In my case I has explained in my letter to consulate that I wil be taking care of my parents expenses when they are in usa and will make sure they will return back to Nepal before their legal stay is over. In addition to the letter, I had sent w-2 form, three recent pay stubs, my bank balance in the USA which was less than 10K, relationship document (father/mother and son/daughter), and visa application.
I also did for my inlaws. I did in a similar way. I asked my inlaws to include my letter to consulate office, my pay stubs, tax return document, bank balance and relationship document of my wife and her parents. it worked for us. I really do not think huge bank balance or property will enhance the chance of getting visa. A proper documents in order and acceptable answer during interview are important factors in my opinion and experience. Note that, in both cases I communicated with my parents and inlaws before the interview and told them what to speak and how to speak with them.
