Defrauded

My father was a savvy business man and did very well for himself. I am the youngest of three siblings who were in line to inherit after my father's death. I have a older brother and a half older sister. My father passed away a few years ago and we asked about our inheritance and were told my dad had left nothing even when we heard he'd left a insurance policy where my brother and I were named yet were told it was funeral arrangement money. I know my father had a will and we were named in it yet after his death we weren't notified in any way. My older half sister inherited it all. We were told she had sold our dad's property which consisted of a bank post office and doctors surgery out in India which sold for 20, million rupees which converted is over 2, million pounds. My brother was told that she was asked about other children in the sale of property she lied and told officials she was an only child. She made my dads life hell and worked her hardest to keep our dad away from our lives and pushed us out. I'm infuriated that this has been done to us all our lives. We need counsel on how to go about this matter in a legal manner. Any advice will be appreciated thank you for your time. Zarina