A Question on Compensation/Family Law

Hello, my mother has come under a certain situation concerning her biological father. We have a family friend to represent us in this case, but I wish to get a second opinion. My grandmother died when my mother was very young, so my grandfather sent my mother to live with a family which were friends of his at the age of 2.This was since he could not afford to upkeep my mother and aunt. He only saw my mother on occasional weekends. When my mother was 18 she was formally adopted by this family. Then my mother met my father and fgrdually they decided to get married, when my mother told her ciological father he disowned her. When the adoptive father of my mother died and left my mother a very large part of his fortune (by turkish law). Now 26 years after, my mother and her biological father were reunited, mainly for the fact of my mother and aunt wanting to see eachother. After, her biological father had a stroke and is left ill. So 3 days ago there was a phone call telling us that my mothers father and sister are suing her for the fact of her "not being morally present for him". Well I beleive that was what the case was being opened for. It is also ment to be for private healthcare for her biological father. He is sueing for a very considerble amount a month, yearly it will amonut to 12% of my mothers intake.

I understand this must seem like a fairy tale, but it is very true. Overall, my mother was adopted by another family, her father told her that she was not his daughter no more for marrying an englishman and now after 26 years he opens a courtcase. Would my mother be liable?

PS: He doesnot seem in any financial trouble, plus my aunt being well off aswell

thanks