Visitor Visa - B2

Dear all, Apologies in advance for the long post.
I had applied B2 visa for my brother (1 month), mother and sister (6 months). Interview was on 9 Feb 2018 and got rejected so highly disappointed. Kindly guide as I want to reapply just for my mother and sister. We lost our father in Oct 2017 so wanted my family to have a break and change in environment. They have to be back in India by Sep 2018 for my fathers 1st death anniversary rituals in oct 2018. Brief about the interview on 9th Feb below:
question to my brother:
1. What’s your salary? I get xxx per annum ( approx 6 lakhs per annum)
2. Who stays in USA? Sister, brother in law and niece
3. What do sister and brother in law do? Sister homemaker and BIL Business Development representative in xyz company
4. Have you travelled internationally previously? No
5. How long you planning to stay? I plan to stay for 1 month, have to return to work. Mother and sister for 6 months after which they will return for our fathers death anniversary rituals
6. Is your father going to travel with you? No, he passed away
7. ( Pointing to my sister) what do you do? ( my sister is a special child with ecr passport, she is 34 years of age but has the IQ of a 9/10 year old kid. Manages all basic responsibilities. So she’s dependent on us and stays with my brother and mother ) My brother responded saying she’s not that fluent in English so I can answer on her behalf. VO said oh ok. My brother said, she can do all basic responsibilities on her own but on critical decisions dependent on us and we take full responsibility of her.

Then VO took a couple of minutes to document, said you do not qualify for the visa and handed over form 214b. VO had rejected 3 previous applications before us.
They did not ask for any supporting documents. We have our own house in Hyderabad, 2 properties and 1 plot in hometown. Besides that our bank balance and no mortgage. We had mentioned our mother would pay for trip expenses in ds160. She would have paid for international travel and all domestic expenses in USA my husband would bear. I am on H4 and husband on H1B.

I plan to reapply for my mother and sister with the interpreter option in March/ early April 2018 as weather is conducive in summer for my mother. Kindly guide what could be done differently this time.

1. I plan to apply for 5 months May to Sep instead of 6 months like earlier as they have to return before October.
2. Not applying for my brother this time as he won’t travel.
3. I am expecting my second child (first is 2.5 yrs toddler now) in August end so is it ok to mention that they would visit in May / June to tour a few places before my baby shower in July and then be there with me during childbirth. After things settle a bit with support system, will return in September.

Many thanks in advance for all your guidance