• Unpartitioned ancestral property - son not party to father's gift deed

My grandfather (GF) had about 50Ac of agricultural land with no children. He adopted my father. My grandmother (GM) has got a sister and she got a daughter (i.e GM’s sister’s daughter - GMSD). This GMSD lived a few years at our home when she was young. However, she was not adopted. She got married by her father at her home in 1973.
It came to light that there is a gift deed executed by my GF in 1975 giving two acres of land to this GMSD on the occasion her marriage. Out of this GMSD sold away 1 acre in 1977. Around the same time my GF paid money to GMSD and bought back the remaining one acre but no document executed for buy back. My GF apparently sent messengers to GMSD to come and execute the document. However, she evaded to do any deed. She never came to our village to press for possession as she was already paid money and we are in possession for last 45 years. My GF passed away in 1992. 
She got a Pattadar Passbook from MRO in 1997 behind our back based on the executed gift deed and in Records of Rights (ROR) her name now. This one acre is a part of a piece of 10 acres of land and there was no subdivision done until now. Now she approached the revenue authorities complaining that her father ( i.e my GF) has gifted her two acres our of which she sold away one acre and the remaining acre is being cultivated by us illegally all these years and seeking the help of revenue authorities to help her. She did not go to civil court.
We plan to file a suit and consulted lawyers. The approaches that came up are:
1.	Since the land is ancestral, gift deed is a void ab initio as there was no partition nor my father consulted nor a party to document. THAMMA VENKATA SUBBAMMA v.THAMMA RATTAMMA AND OTHERS and also quite a few number of cases at different high courts.
However, the risk in this is the court at admission stage itself, or at the instance of other party may say it is time barred.

2 Since my father is not a party to the gift deed he never knew that it is a gift. He was under the impression that the deed was only for one acre and that too it was a sale and not a gift. Now he came to know about the gift at MRO enquiry notice and seeking court to declare that the deed is void ab initio. Here the risk of limitation is reduced. The glitch is – the other party would press to say that it is time barred as my father knew it when he doesn’t have his ROR in 1997 for full 9 acres. Of course there are lands which missed to go into our ROR and we did not notice which are in ROR and which not out of total 50 acres that the family has got.

•	The backup is adverse possession.
•	The adjacent owners can give evidence that they never saw GMSD farming land by herself through anyone in these lands in the last 45 years
•	There were few other sale/gift deeds executed jointly by my GF and father until late 1980s and there was never a partition taken place.
In view of the above facts which approach sounds better? Are there any other better approaches?