Thank you so much Sir. My persistence with IELTS has finally paid-off. As always, your advice is highly appreciated. The letter my brother-in-law provided was from "Community Service's Child Services by the Region of Waterloo". I asked him to provide me with the online bank statement for my sister and i will include it with the above letter, but he insists he will get more government papers in couple of days.
My other major concern is, my father's name in my citizenship, passport and birth certificate is according to his citizenship. However, my sister's is missing the last part which indicates our caste, not the surname in her documents. In the local context, it doesn't really matter but I don't know how much impact it can have on my application! Hence I have collected scan copy of my sister's passport, birth certificates for both of us (Original, Translated and Notarized), Relationship document between parents, my sister and I. Furthermore, I have prepared a self-affidavit for confirmation of my father's name along with confirmation letter from local governing ward office stating both the person are same. My mother's name is the same in both birth certificates. Could you please let me know if I have covered fully for my father's missing last name (caste) issue here? Thank you so very much once again and have a great day.