Can a person buy property more than its value authorized by govt ?

hi sir..can u please give ur value advice fohi sir..can u please give ur value advice for the following question. my father and his close friend build two identical houses sharing party wall in 1988. now my father was expired and his friend wants to sell their house to third party but we dont want another co-owner so we decided to buy it for 15 lakhs and asked him to sell his house to us.he refused to sell it to us becoz real estate broker brought a party ready to buy it for 20 lakhs. the government value for our house value is 7 lakhs. we came to know about this value when we took loan from bank on my house. is there any possibility to buy it for 15 lakhs???? thank u sir. am looking forward to your valuable advice