1) Since the land belongs to your great grand father, it is an ancestral property in the hands of your grand father, your father and uncles and their siblings.
2) Also in all likelihood, the property standing in the name of your grand father was also obtained through funds derived from ancestral property and hence the properties standing in the name of grand father will also assume the character of being ancestral property.
3) Assuming your great grand father was alive in the year 1956 and his daughters(your grand aunts) were married prior to 1986(prior to amendment of Hindu succession act by Shri.N.T.Rama rao) , the property will vest on your grand father only, but it will still be ancestral property. If daughters (your grand aunt's) were not married till 1986, then the property will vest with your grand father and his sisters(your grand aunt's).
4) Assuming your grand father alone was vested with the ancestral property, The property by virtue of it being ancestral property will be governed by Section 6 of Hindu succession act and as such your grand father can execute a WILL pertaining to his share of property (after his share in property is computed under Section 6 of Hindu Succession act). i.e grand father, your father, your uncle(father's brother), 2 sons of your uncle, 2 children of your father(i.e you and your sister) and grand mother
5) Your grand father would have got 1/8 share of ancestral property and he can execute a WILL to the extent of 1/8 of his share of property Only.
6) Since your uncle claims that his in-laws gave 1 lakh to your grand father, it is actually a dowry received by your uncle and as such it will be illegal to claim the said amount in the first place. Also the said money can never be accounted for in the year 2018 as your uncle if at all wanted to claim his share of property equivalent to 1lakh should have claimed the land way back in the year 1985. Law of limitation will NOT permit the said claim of 1 Lakh by your uncle and hence you can ignore the same.
7) Also any monies so contributed to common hotch pot of the ancestral family properties, cannot be claimed at a later point of time and it is only the present state of properties that are liable to be partitioned and hence the claim of your uncle will not pass the test of law.
8) Assuming you file a suit for partition in the court, the properties will be divided in equal shares between all of the co-parcenors( i.e grand father , grand mother(if both are alive), your father, your uncle(father's brother), 2 sons of your uncle, 2 children of your father(i.e you and your sister)
Hope this information is useful.