Since this property was allotted to Mr. Yadav and subsequently the sale consideration amount was paid on behalf of Yadav to GDA, Yadav became the absolute owner of the freehold property.
Since your mother, who was just a GPA to the principal, namely Mr. Yadav, upon her death, the GPA deed stands automatically revoked or infructuous, thereby the property reverts to Yadav and he becomes the absolute owner of the property to sell or transact with the same without the GPA's aid.
However since the property is in your possession and enjoyment, it is better to request Yadav to execute a registered sale deed in your favor since you and your siblings are the legal heirs of your parents.
The will bequeathing the property in your favor made by your parents in respect of this property is not valid in the eyes of law since they do not have marketable title to the property.