query regarding property

Hi am abhishek from mysore.
My Father and grandfather both had been allotted with a site next to each other from the government through SC ST welfare dept in 1990s..
As we had joint family all members including brothers of my father decided to build a house in site allotted in2000s.. By mistake they started construction on my father's site..
So In return all including my grandfather and brothers of my father(except sister) had signed on a document 10-15yrs back to give the site of grandfather to my father in exchange..
Now my grandfather is deceased in 2016..
is there any prob for us to build house in the site, as sister of my father has not signed the document at that time..???
Is her sign necessary..??
If necessary.. Now wat steps we should follow now..???
Please suggest me

On hich deed did your grandfather and your father brothers sign? Is it registered? Did they take permission for construction from Government?  state required info for replies.

On a normal bond paper they have signed.. But it is not yet registered.. We can get khatha done to my father's name in panchayat office through the employees there.. As our site is in rural area..
For the construction of the house they have taken govt schemes financial help given through village panchayat..

As of now, apparently, there are no problems for more clarification contact a local advocate and get his opinion showing all documents, as he will assist you as and when you approach.

As of now, apparently, there are no problems for more clarification contact a local advocate and get his opinion showing all documents, as he will assist you as and when you approach.

Show all relevant documents to a local lawyer for better appreciation, guidance and proceeding.