Need help with situation

I’m in a difficult situation regarding a property in Indore. The building has two separate registries: I own and live on the second floor, while my sister’s children live on the first floor. Sadly, both my mother and my sister have passed away.

Even though we have separate property registries, the municipal office still treats the building as a single unit for tax purposes. Because of this, I am forced to pay the full property tax for the entire building out of my own pocket to avoid being marked as a defaulter. I have spoken to my niece and nephew about paying their share, but they refuse to contribute, claiming that since it was their mother's home, they don't care about the taxes.

I don’t want to be a defaulter, but I cannot keep paying their share. Does anyone have advice on how to handle this situation, how to legally force the municipal authorities to separate our tax liabilities, or how to get my family members to contribute?"