Ancestral property

My grandfather died before 20 years intestate leaving his property a house site without will or settlement to his childrens he had two sons and wife as legal heirs, I my self elder sons son, my father( elder son) and my grand mother is alive and my uncle( younger son) died last year, Before 5 years my grand mother made a settlement in favour of my father by settling her 1/3 undivided share in the house to my father by a registered settlement deed, Now my father wants to settlle his 2/3 of his share(1/3 inherited by himself & 1/3 by settlement from mother) to me by settlement , To my father we are 3 childrens 1 son (myself) and two daughters ,whether my father alone can do the settlement of his 2/3 undivided share to me or my sisters should release the property,my two sisters claiming that the have rights over the grand father property and it is ancestral property they should sign the document. what is the procedure to get settlement from my father 2/3 of his undivided share without consent from my sisters if i get the settlement from my father after his period whether they can challenge me legally.