Land distribution b/w the sisters after mothers death

My grandmother having two daughters , my mother is the younger one, few days back my grandmother died , and the land was not distributed bcoz of my grandmother's decision to share after her death , actually by the acceptance of my grandmother we built a house in the front part of the land as our property is long but not that wide ( as per our little knowledge the land would be shared front and back, not side by side) Now, my mothers sister (ie., elder one) making a scene by approaching a lawyer and blackmailing us that theyll sent a notice to us from court that they want share in our own home which is our property, and she want the front portion of the land in which we had built, and she is claiming that we had to take the back portion, we don't have any documents for that house we've built, but there's a document which is given by my grandmother on my mothers marriage which contains the matter regarding land will be shared equally to both the sisters. now what we have to do, it's my appeal to give us your valuable decision