Visitor Visa - B2

I recently applied visitor visa for my sister and her 1 year old daughter. Her husband works for a IT company. My sister is a physician but not working currently. We applied for tourism purpose and I will be sponsoring her and her daughter with all expenses.
She finished all the formalities and stand in the line for interview along with her daughter.
She was 4 th in line. All three before her was rejected.
One person applied for work visa to work in an airport and gave elaborate answers to each question asked.
Other person – visitor visa but was hesitant in giving answers
Third was old couple with young son- when VO was asking questions in English, son volunteered to answer for his parents since they don’t know English. He was anxious too. VO rejected saying you cannot answer for them and they have to come back for a telugu interview
4th is my sister. By this time, she has lost hopes that she will get visa. But was thinking he may approve hers, given mindset would be to grant one after few rejections.
VO is not smiling at anyone.
Sis gave the documents

VO: why are going to US
Sis: To visit my sister and her family. They are planning a road trip in summer and want me and my daughter to join
VO: what does your sister do?
Sis: she is a physician
VO: when did she go to US?
Sis: 10 yrs ago
VO: Has she been a physician since then?
Sis: Yes
VO: But she only started working since last year?
Sis: Yes. That’s because she has to do her residency and fellowship to work as a physician.
VO: will you work there?
Sis: No
VO: How long are you planning to go?
Sis: 4 months
VO: 4 months?
Sis: Yes because my sister’s vacation is spread out over these months and she is planning for 2 road trips
VO: what does your husband do?
Sis: He works for xxx company
VO: is he not coming with you?
Sis: No. he cannot get that much vacation.
VO: Both of your visas got approved.
Sis: Thank you. Say bye (to her daughter)
Niece waved bye and VO finally smiled and waved back.
He did not look at supporting documents at all. He just verified my information online while doing the interview.

Points to be taken:
1. Be confident in your answers
2. Answer to the point. Don’t elaborate. VO don’t have too much interest in what you like about U.S
3. If you don’t know English or understand American accent, go for local language.
4. Never act nervous or be desperate to get Visa. That can count against you. Be calm and confident. (since my sister is nervous to start with, I told her this)
5. If VO is serious or rejecting visas to people before you (especially compared to other VO), don’t lose your cool.
6. Be well prepared for answers.
7. Don’t you too many ‘Sir’s and ‘Madam’s. U.S people are not used to that.
8. If you are young and have children, do not leave children behind for a tourism purpose.

Both my sister and her daughter got multiple entry 10 yr visa.