1) You first need to file a criminal complaint against the persons who created the false, fabricated GPA and also the Real estate firm under sections 419, 420, 465, 467, 468, 471, 120-B, 34 and 114 of the Indian Penal Code in the police station or file a private complaint under the above sections in the court under section 156(3) of the Code.
Section 419 : Punishment for cheating by personation
Section 420 : Cheating and dishonestly inducing delivery of property
Section 465 : Punishment for forgery
Section 467 : Forgery of valuable security, will, etc.
Section 468 : Forgery for purpose of cheating
Section 471: Using as genuine a forged document or electronic record
2) Your should also file a civil suit in the District court and ask the court to cancel all the sale deeds and also ask for declaration of your ownership and also a permanent injunction against the real estate firm and several individual plot owners.
3) We can ask the courts to issue directions to Forensic labs for comparison of signatures and establish forgery and also award punishments for fraud, forgery
4) As long as you are on the right side, law will protect you and you need not worry about the size or money power of real estate firm.
Hope this helps.