Proof of Payments?

Missouri My father(deceased) made a loan with a signed promissory note,which went to my brother,my sister and me in the event of his death. He told us the party he entered into the agreement with was behind on payments. All I have is his bank records as proof of any payments made. As far as I can tell there a several payments lacking. I offered to pay for their cost of getting cancelled checks, but they would not oblige. Now they want the deed for the property and signed sworn affidavids that they made all the payments on or before the date they were due . I know for a fact that there were several payment made late even after they started paying to me.
Do I have any legal right to demand proof of payments?

You do yes; you can argue the payments have not been made and ask them for proof. And you need not cancel the note until you are satisfied.