Reclaiming of Property after 10 years by illegitimate son

Hi , My father purchased a property on August 2014 from xyz . A few weeks later a civil property case was registered against our property .It was done by one of the illegitimate son from 4th Party above in family tree hierarchy . His father had extramarital affairs with his servant and he is the son of their relationship . After his father death , his father's legitimate wife along with all her sons signed in the property document and sold the property to other party (3 rd above in family tree ) . And later it came to us . He has put the case on the legitimate family saying he needs some share , and he is creating problem during building construction . He along with BBMP (Bangalore municipality corporation ) has stopped the construction . BBMP officials are saying that since complaint is raised in our property ,The property can be stopped constructing . What can be done now ? Should we wait till the case judgement ? Does he have upper edge to the case . Can we resume construction by involving Police here? How many years does it take for a case to get cleared ? P.S : He has filled the case 10 years after the legitimate family has sold the property .