Money and Property being Looted by Elder Sister

Hi, I stay in a different city due to my work. My parents have certain health issues and hence they are home-bound. My elder sister and her husband stays nearby and manage all their finances (all the debit cards are with my sister and her mobile no. is also linked to all the accounts). Even after 7 years of my parent's retirement, I have not been informed about the account numbers, the limp-sum they received at retirement and monthly pension amounts. My parents both worked at good positions under Central Govt. I can guess that they together earn at least Rs. 75K monthly as pension and also have more than 50 lacs at least as fixed deposits but my elder sister refuses to share the savings account no. or the exact pension amounts. Moreover, she now has the keys of one vacant property which my father had purchased. My elder sister and her husband works at very junior positions at some local company but their lifestyle is way above their affordability which made me to worry about these things. Given that my parents are still alive (but not in perfect mental state), how do I ensure that I am not cheated of their properties and money. Can I approach the banks with my parents' Aadhar card or PAN? I will not be able to relocate anytime soon to my hometown. Regards, Dwaipayan