Loan amount return dispute

ye query mere uncle ka case hai -- 1.uncle ne kisi dost (jain sahab) se paise udhar liye they cash me aur time to time wapas bhi karte rahe. 2. udhar lete time uncle apne letter head p likh k diya k itne paise itne byaj p le raha hun..( uska sample image main bejh raha hun) 3. par uncle k paise lautate time jo recieving thi vo kho gayi h na koi record h aur uncle ne bh paise cash me hi diya tha 4. 2017 me jain sahab ki bimari k karan death ho gayi , to jain sahab k bete aur damad ne uncle se pucha k apne kitne udhar liye they to uncle ne kaha 14 lakh but use time to time utar diye they exact amount dekh k batunga 5. jain sahab k bete ne kuch jaan pehcahn k logo k sath aur vakil k ghar uncle se likhwa liya k 14 lakh bakaya h aur uspe witness k bhi sign kara liye (iski koi copy uncle k pas nah h ) ye june 2017 me hua 6. uske bad uncle k beto ne hisab lagay to kul 7 lakh bakaya nikla ,,,uske bad unhone jain sahab k bete aur damad ko apne ghar bulaya aur kaha ke haamre family relation h par apne hamare pitaji se jabardasti 14 lakh likhwa liye jo k sah nah h aur apka sirf 7 lakh bakaya h. to unhone bola thik h ap 7 lakh wapas kar (iski voice recording h uncle k pas) 7. uncle k bete ne 2018 me 2 lakh lauta diye cash me , aur whatsapp kardiya jain sahab k bete ko k ab 5 lakh bakaya h ,,2019 me paise na hone k karan vo kuch paisa na de paye 8. 2020 me jain sahab k damad ne uncle dwara likha hua bhi bejh diya whatsapp p (jo ki ek tarah ki dhamki lagi) 9 ab uncle ko lag raha h ki bache hue 5 lakh dene k bavjood bhi agar vo 14 lakh wala parcha leke khade ho gaye to hum kya karenge. aise situation me kya kiya jaye ? 1. kya jo uncle ne likh k diya uski validity h legally ? 2. kya uncle ye bol de k humne hisab k mutabik 7 lakh wapas krdiy h . 3.kya uncle complaint kare ki jabardasti 14 lakh likhwa liye 4. kuch aur better opinion ?