Need Clarification on Visitor Visa Doubts

[mghosh]

Hi....................................I am in H4 visa and planning to invite my parents. I have few doubts regarding visitor visa .

1) My father is working in research and development under the ministry of defence . I need to know that is it too difficult to get visa for the people working in this field.

2) My mother is a house wife. Will it increase the chance of rejection if my mother attends the visa interview alone?

3)If they get 6 months visa now and in case cannot come to usa within that period, will there visa application be rejected when they apply next time?

Any help is highly appreciated.
Thanks.

[immihelp]

1. May be.
2. No.
3. No.