The property is reportedly jointly owned by husband and his deceased wife.
As far as the share of the deceased wife is concerned, it will devolve on her own legal heirs consisting her own children and her husband.
The children of the second wife neither the second wife would be entitled to any share in the property that belonged to the deceased wife.
You have to obtain a family tree certificate or legal heirship certificate in respect of the class I legal heirs of the deceased wife and all those legal heirs have to execute the registered sale deed jointly in your favor.
If there are any minor child(ren) to the deceased wife, then the father/guardian should file an application before court competent seeking permission to sell the share of the minor child citing the reasons that he relies upon to seek this permission.
After obtaining the permission from court with regard to the share of the minor, the father of the minor child can execute the sale deed ion behalf of the minor child too.
Whatever, you may obtain a proper legal opinion from an experienced local lawyer and proceed only if it is recommended.