1.Was the property ancestral or self-acquired property of your father.
2. Whether your father died intestate(without leaving a WILL)
3. Assuming that the property was self-acquired property of your father and had died intestate, then the combined Katha should have been in the names of 'Y', 'A'', 'B', 'C', 'D','E', 'F' OR 'Y', 'A', and 'B' should have executed relinquishment deed or NOC in favour of C.D.E.F, then only the combined Katha made in 2004 in the name of C.D.E.F is legally valid.
4.You have stated that in 2015, 'Y' and 'A' gave GPA to 'C' to execute release deed in favour of D.E.F. If the combined Khatha made in 2004 in favour of C.D.E.F is legally valid, what was the need for 'Y' and 'A' to give GPA to 'C' to execute release deed after a lapse of more than 10 years.
5.From the above, it can be presumed that 'A' is within her rights to challenge the non-inclusion of her name in the Combined Khatha issued in 2004, if she has not executed relinquishment deed or NOC in favour of C.D.E.F before the combined Khata was issued in the year 2004