Visitor Visa - B2

Hi,
My in-laws attended the interview today morning and were rejected saying no bank balance.

These were the questions asked:
1.visiting purpose?
-to visit daughter and son-in-law and for visiting places.

2.who do you do?
-Business.

3.income?
-Since my in-law has a small business, he answered slightly less Rs.2 lakhs as yearly income as he does not have any IT returns.

4.any bank balance/Fixed deposits?
-since he doesn't have any, he said NO.

since i'm the sponsor for my in-laws' visit, i gave all my required financial documents, showed more 17K savings and other things, i thought they would take my finances into consideration. They did not even allow my in-law to say anything after the last question. He wanted to say he has land, own house, shop and has daughter(married) with grand children and a young son (working) to get married. But they dint allow him to talk anything and said you are not qualified and dint see even one document. My in-law said 3 couples before him and 2 after him were all rejected and 3 of them had the same reason - bank balance!

I'm trying to re-apply in a couple of weeks again showing some bank balance.

My questions:
1. how soon or late do we need to apply again?
2.how much bank balance do my in-laws need to show?
3.what if only my mother-in-law appears for the second time? will she be rejected/?
4.will the chances to get the visa better if my in-laws show as self-sponsorers, instead of me being the sponsorer? If yes, how much finances do they need to show?

Please reply soon,
Thanks.