Below are the answer to all your questions:
Answer 1: Earlier, according to the ruling, a daughter can avail of the benefits granted by the amendment only if her father passed away after September 9, 2005. and the daughter is eligible to be a co-sharer only if the father and the daughter were alive on September 9, 2005. However, on February 2, 2018, Supreme Court has made it a general rule that a daughter, living or dead, on the date of amendment will be entitled to share in father’s property, thus making her children too to claim this right. So your father's sister children has equal rights in grandfather property 1/3rd share.
Answer 2:
a) No its not valid, there should any agreement between two brothers against this property.
b) Need to know why the X person has filed case against your father and why the decree was given in favor of X Person. need to review the history of this case to provide perfect guide line.
c) Your uncle is responsible for 1/3rd share of his own.
d) If we assume that the 7 acres land were disputed from your grandfather's time then we can minus that 7 acres from 20 Acres so it will be 13 acres and this will distribute equally among 3 legal heirs. each will get 4.13 approax ( Four Acres 13 guntas).