1. The share in the property of your deceased husband shall devolve on all his legal heirs consisting you, your children and his mother (if alive).
Hence all the other legal heirs have to execute a registered release deed relinquishing their rights unto you which will make you an absolute owner to sell the property with full marketable title.
2. You can apply for legal heirship certificate from the revenue department with your jurisdiction by producing the death certificate along with the application.
succession certificate shall be provided by court if you file a case seeking the same and it shall be applicable for the movable properties lying on his name at the time of his death.
3. After getting the property rights fully on your name, you can apply for mutation of records which would hold you as an absolute owner to the property with marketable title to enable you to sell the property properly and legally.