You can indicate the full name of the borrower's father-in-law, the purpose of the matter, the amount (chinese numerals, Arabic numerals, Chinese pictographs), the date of loan, the full name of the debtor's daughter and son-in-law (handwritten), the time of coinage (year, month, day) and so on. After verification by both parties, the lender draws a piece (hand model or seal), and witnesses of both parties sign the piece, pad it with blue and copy it in triplicate.

Shanglian, delivered to creditors for preservation;

Zhonglian, witness preservation;

Downward, the debtor keeps it.

If the debt is repaid in installments, the creditor shall sign for it and hand over the receipt to the debtor for safekeeping.

Pay off the debt and destroy it after triple reconciliation.

......

The model essay is as follows:

(Writing in Chinese)

Title: iou for down payment of house purchase

Use: On 20th/month/month of 20 1 year1year, I borrowed money from my father Li XX and my mother Liu XX (Yue's) and paid a down payment of 654,800 yuan, with no interest. From today, daughter Li XX and husband Wang XX will pay off all the money in three stages.

Words are empty, words are evidence, and this certificate:

Lender and creditor: (signature) Li XX, Liu XX ID cards Li XX 122...5643, Liu XX 160...5364.

Loan amount: RMB six hundred and fifty-four thousand eight hundred Yuan only. 654,800.00 yuan.

Debit and debtor: (signature) Li XX, Wang XX ID card Li XX 122...5643, Wang XX 160...5364.

Notary of both parties: (signature) Zhou XX

In triplicate, one for each party and destroyed on the day of reconciliation.

Date of word formation: Xinghua Village, 4: 07 pm, Year of the Rooster, Year of the Rooster, Ugly Moon, Renzi Day, December 20th17.

......

Or, ask a lawyer to establish evidence according to legal requirements and conduct judicial notarization.