Custody Of Child And Depositing Of Money In Her Name

I am Located in Noida (UP). I seek opinion and a way forward on the facts narrated. My Niece Mrs “A” was residing in Hyderabad with her husband Mr “B” at Hyderabad in their own house having joint ownership of 50%. She was 7 months pregnant and came to Allahabad in Uttar Pradesh in her mother’s home Mrs “C” for her delivery in the month of March 2021 along with her 3-year-old daughter Miss “D”. She contacted Covid in the month of April and was hospitalised in Allahabad but unfortunately, she expired leaving her sole daughter “D” at her mother house Mrs “C” and in her custody. My nice Mrs “A” was working as software professional and had left Rs 25 lakhs in FD, Rs 30 Lacs in LIC Policy and Rs 10 lacs in PF Account and in all these accounts she has nominated her husband Mr “B” as nominee. My sister Mrs “C” want to have custody of minor girl Miss “D” as she knows that Mrs “A” in -Law are greedy and will ill-treat the minor girl “D” and will try to marry Mr “B” and after her father marriage.