Hi Nitin,
Yes, your mom must do her medicals for a super visa. She can either do this up front before applying.... or wait for the visa office to send her instructions to do the medical exam.
Your mom must show that she has strong ties to India: Property or land ownership/lease agreement, employment or business, family ties, previous travel history, good financial situation, etc.
Your sister must submit the documents mentioned by MARCHIE.
It's not possible to predict the chances of approval. Do prepare a good application with solid evidence + go through the CIC link in the previous post
Cheers