1. Your friend's grandmother can not execute an Will for the entire property of her husbamnd, who died intestate, in favour of her two sons since she is the owner of only 1/3rd of her deceased husbands property. The remaining 2/3rd of the property is equally shared by her two sons,
2. Inview of the above, the said Will is invalid and son S1 should contest the probate application,
3. However, if the Will of the Grandmother is accepted, then mere signing the building plan for getting sanction does not entitle S1 to claim 120 Yrds of the property in place of 100 yrds willed to him,
4. In the above case, S2 shall have to execute & register a Gift Deed for conveying the title of 20 yrds of the property to S1 to regularise the aggreed division.