My father and mother passed away, leaving behind my sister and me as the legal heirs of our jointly owned flat. I’ve been paying the EMIs alone. Can my sister claim a share of the flat? If yes, what percentage is she entitled to?

Yes, your sister can claim a share of the flat. As legal heirs, both of you inherit the property equally, meaning your sister is entitled to a 50% share of the flat. The fact that you’ve been paying the EMIs does not give you full ownership.