will as per sharia- islamic act

My father made a will transferring his entire share of the property in the name of my step mother leaving nothing for my mother and sisters and shortly expired. We have challenged the legality of the will and understand that he cannot bequet his entire share except 1/3 of it. Now we want to know whether the will, will be declared null and void by the court due to wrong share ration and will my step mother be entitled to 1/3rd of the share automatically? Or will the entire will be void and his entire share will be divided as per muslim law.?i