1. you will have to file a suit for specific performance of contract based on oral agreement
2. till today the friend of your FIL has not denied that he has received money from you
3. he has also not expressly denied that the money was transferred to him by you for purchase of his property
4. you must be having the call records to the FIL and his friend. That can be used in evidence subject to providing the necessary certificate under 65B of evidence act
5. issue them a legal notice with copy marked to police
6. i know that since your FIL is involved you may be a bit reluctant to take legal steps against him
7. but law is oblivious to all that. If you have suffered a legal injury then you must pursue your legal remedies at the earliest to prevent your claim being transformed into a stale claim
8. courts lean in favour of those persons who take actions swiftly when their legal rights are infringed
9. courts abhor those persons who sleep over their rights and do nothing and approach the courts belatedly