Oral statements are not completely disregarded in law but it is very difficult to prove the validity of an oral statement. Assessing from your facts, I am assuming that the first distribution of the property was done by proper documentation while the 2 acre given to your wife was done by an oral statement. The issue is that to take the matter to a Court, your wife will have to prove that her father made a statement like this. For that you will have to employ supporting evidences from witnesses, video or audio files etc to show that the father actually made such a statement. I understand that the possibility of procuring such an evidence is very limited and therefore it will be difficult for your wife to take her brother to Court to make a claim for the 2 acres.
You can look into the possibility of dividing the 7 acre for succession. The 7 acre kept by the father, after his death, becomes an intestate prperty if ther is no will. Therefor the 7 acre property will be subjected to the Hindu Succession Act. Under the Hinduc Succession Act, all the children of the deceased have an eqaul right over the property. After an Amendment in 2005, a daughter will also have equal right over the property. Therefore, after the father's death, the 7 acre has to be distributed equally between the two daughters and the brother. The only issue can be if the said property is an agricultural property. If it is an agricultural property then the local land law of your state will apply for succession. Unfortunately, some of the state laws are not gender neutral and give the entire property to the male desecendants. Therefore, first of all identify the nature of the property, which can be done from the District Collector's office. If it's an agricultural property, check the law applicable in your State to identify if it allows daughters to inherit agricultural property. If it is not an agricultural property then you can file a suit agaisnt your brother under the Hindu Succession Act to make a claim for the equal distribution of the 7 acre property.