Hi
1) Since the properties were acquired by your grand father, these are self acquired properties of your grand father and as such his properties will devolve on his legal heirs under section 8 of hindu succession act.
2) Legal heirs under Section 8 of Hindu succession act are son, daughter, wife, mother, children of pre-deceased son/daughter.
3) Since the properties are self acquired of your grand father , these are not ancestral properties and as such you do not need to worry about Hindu succession amendment act 2005 as the same is not applicable to you.
4) Even assuming for a minute that these are ancestral properties, hindu succession act was amended in the year 1986 by Shri.N.T.Rama rao , where in he granted equal rights to both son's and daughters in ANCESTRAL PROPERTY also in the state of andhra pradesh.
5) So technically the 6 acres owned by your grand father will be divided in to 3 equal shares i.e 2 acres each to sons(2 Acre*2 sons) and 2 acre's to daughter.
6) So your elder uncle is right in executing 2 acres to you by virtue of a gift deed . Yes , the question of younger brother not signing the gift deed is a concern, but since the elder brother has gifted you 2 acres out of 6 acres, the younger brother has no other choice other than to consent to the gift deed executed by your elder uncle.
7) So you will win the case even if your younger uncle files a suit against you.
Hope this information is useful.