This is my response to you:
1. Do you still have the joint venture agreement? Is it signed by all the 25 people? including that friend?
2. One will need to go through the joint venture agreement;
3. It is not possible that the appeal is pending for 16 years;
4. Your lawyer should have mentioned the matter, told the urgency of the case and get it disposed of soon;
5. You can file a separate suit against your friend for cheating you;
6. Even if the agreement is not registered still has evidentiary value and can be used against that one friend;
7. You can also file an FIR for cheating and criminal breach of trust, both punishable under IPC, to the nearest police station;
8. Take interim orders against this chairman and get a stay on property;
9. You should collect all evidence in your favour and how you had mutually agreed to purchase etc.;
10. In law, even oral contracts are binding as per the Indian Contract Act;
11. Therefore you have merits in the case and the judge out of good conscience should act in a fair and just manner.