• Property purchase legality issue

We purchased a property in Nov 2013, we had checked and obtained all necessary legal documents and also availed a bank loan for the same. Before the purchase,we had given announcement in newspaper also. Since then, we have been paying taxes and also changed the patta name to ours. Previously, the property actually belonged to brothers of one family inherited via their mothers will- which states that the property goes to the male members of the family, and their male sons.
Elder Brother is A (owns 1/3rd of the property)
Younger Brother is B (owns the rest)
A gives a settlement deed of his share to B in 2011 , after which B became the sole owner of the property, and then he sold it to us in 2013. Now in 2016, a woman claiming to be the daughter of A says that her father died in 2008 and never gave settlement deed to B and questions how can A give settlement deed in 2011, as he expired in 2008. Her mother is alive ailing. Also accuses B has forged that registered settlement deed, denies the signature, photograph in the settlement deed that happened between brothers. Now, she has issued legal notice to all the parties concerned demanding money from the seller & buyer for her father’s 1/3rd share, failing which she would press civil and criminal charges.
We are yet to see any documentary proof of any sort from her. But she claims to have her father’s death certificate and property tax receipt which was last paid in 2007.Currently,the seller B is not approachable .Legally, we have done nothing wrong. We are an innocent third party facing these troubles now. 
Our queries :
please advise how to safeguard the property & ourselves.
what should be our first line of action??
Does she have claim in the property because the ORIGINAL WILL statement favours male descendants?
How can we confirm that she is the actual daughter of A ?
will we face any civil or criminal charges?
can the registered settlement deed (between A & B) be cancelled/ proven false/revoked? 
Will this affect our registered sale deed of the entire property?
Usually, How long does these kind of cases run in court?