Transfer deed done instead sale deed and now brother challenged in court to cancel it by refusing the cash payment part

This case is from punjab. My dad did a baiyana of 25L with his brother for 6 marla shop with total deal of 1cr. Its a single 12 marla shop with rest 6 marla owned by my dad and already in possession with my dad. The collector value of the land is 30L written on transfer deed. His brother blackmailed us in doing RTGS of only 30L and rest by cash of 41L and 4L by RTGS in his friends account. I have whatsapp chat where he sent that account info. And said he will give double the baiyana amount if we didn't do so. We were already doing business in that shop for 20+ years and we succumbed. We didn't know that transfer deed will land us in trouble than sale deed. We paid him 41L cash, 4L RTGS in his friends account and rest 30L RTGS in his personal account on the day gift deed got registered. And inteqal got done as well in 2 months. Now his brother has put a fake case on my dad to cancel the transfer deed saying he has not received 45L cash. We only have a retired SHO as a witness and bank statement of cash withdrawal of full 45L on the day of Transfer deed registration. We forgot to take receipt of 45L from him. Can we land in trouble of doing a transfer deed without any stamp paper instead sale deed. He has put a case of cancelling deed and permanent injunction on property. Kursinama is prepared from his brothers side. It has his brothers sign.