Section 15(2) of Hindu Succession Act - Wife died without childer

Case Brief: 1) Mr. A-1 (Late) had acquired agricultural land – under a sale deed registered in 1920. 2) Mr. A-1 had gifted the acquired land to Mr. B-1 (Late) under the gift deed registered in 1945. B-1 is son of A-1's wife sister. It is clearly mentioned in gift deed executed in 1945 that B-1 has helped A-1 in many works & affairs, that is why A-1 had gifted land to B-1. 3) B-1 got married and was blessed with a female child, only child, henceforth referred as B-2. And marriage of the B-2 was performed with Mr. C-1. B-2 & C-1 has no children. In short.....A-1 had gifted land to B-1; B-2 is daughter of B-1; C-1 is husband of B-2; C-1 & B-2 has no children; A-1, B-1 & B-2 have had expired; B-1 & B-2 have no legal heirs in any manner....B-1 is the only son to his father and B-2 is only daughter to her father(B-1). 4) B-1 died issue less, since B-2 is the only daughter to B-1, she got sole rights on her fathers property. B-2 also died, issue less, in 2004. Since there are no legal heirs to B-1 & B-2, C-1 has taken the possession on the property. 5) C-1 has got all land revenue documents on his passbook, paid land tax on his name. 6) In 2007, we purchased this property through a sale deed registered in 2007. Now, in November 2014, wife of grand-son of A-1 sent a legal notice to us & c-1 claiming that 7) Since B-2 died without children, her husband (C-1) cannot be considered as a heir or rather successor Under Section 15(2) of Hindu Succession Act 1956. The property inherited by Hindu women from her parent side should go to the inherited side only but not to her husband. 2) And also claims that since there are no legal heirs to B-2, the scheduled property should come back to her & her sons in reversion. Wife of grand-son of A-1 claims that since C-1 can't be considered as legal heir to B-2, sale deed executed by him in 2007 is avoid. 3) Plaintiff claims that provisions of Section 15(1) of Hindu Succession Act 1956 are not applicable to facts of the case. My Question: Do heirs of A-1 has any legal right on the property as claimed by wife of grand-son of A-1 ? Is there anything we should worry about as we bought this property from C-1, Since he has no children ??