Visitor visa inquiry for my mother

[jank002]

Hello All,

I am inviting my parent to visit me in California this summer. i am on h1b and working in tech company. my elder sister is on H4 and she is married and has 2 kids. i have a married younger sister in india. my dad already has a valid b1/b2 visa. my mother was rejected twice on 214(b):
1. first time in 2009, my sister invited my mother during her pregnancy. i guess, this was obvious reason for rejection. 
2. my parent applied for tourist visa through some local travel agency. trip was very short, like 11 days. which wasn't convincing to VO.

both the time, i didn't pay much attention and wasn't actively advising them throughout the process, including filling ds-160 and document preparation.

this time i am inviting my parents to visit me and i am taking care of all documentation and financial support. I have some question regarding visa application:

1. Should they mention about visiting my sister and my two nieces. as my sister can come to California to visit my parent or they can go to my sister's place. whichever is better to mention during visa interview.
2. regarding refusal info in DS 160, we don't remember exact data of denial. can i just mention year and 214(b) as reason.
3. in DS 160, Q-31 have you made specific travel plan? should i say yes, as we know which dates my parents will be traveling based my dad's leave time. but we didn't book flight ticket yet.
4. how can we show strong family ties and other ties to india. my younger sister in india is married. and both remaining children are in USA. will it be a problem? 
5. As only my mother is going for visa interview, is it better to show my father as sponsor or myself? i have very good bank balance($80k) as i am saving for downpayment on house. my father's annual income is Rs. 800,000 and my mother's income is Rs. 250,000. but they don't have enough money in saving account, they have about Rs. 450,000. 

Thank you for your time and help.