From your contents the following can be observed:
1. The company is not holding a registered title deed on its name, it is having a only a GPA on its name to prove its title.
The GPA is not a title document.
It is illegal to have title in the form of GPA and there is a supreme court ruling on it do declare that the GPA is invalid title.
Furthermore the GPA can be given to an individual and not in favor of a company because company cannot physically enter into any transaction.
Therefore the validity of GPA and validity of title to the property in the name of company itself is under doubt, which can be clarified and confirmed only by scrutinizing the title document held in the company.
2. The company's decision to sell the property has to be decided by the company in a board of directors' meeting by passing a resolution supported by majority of members/directors.
The resolution passed by the company would be recorded in the minutes book of the company. The extract of the minutes of the meeting can be extracted and on the basis of the decision taken in the meeting the company may give an authorisation letter to its staff who will act as the company's representative for conducting all the transactions the company intends to carry out with regard to this property.
3. The resolution has been passed by majority of the directors hence it can be considered as valid, however the the copy of the resolution in the company's letter head along with the original authorization letter has to be produced by the company for verification.
All the above process are to be carried out diligently and with proper scrutinisation, hence it is advisable that instead of seeking piece meal information from forums like this better you may obtain a proper legal opinion from a local experienced advocate and proceed only if recommended.