Owner Financing

My Mother is going to be doing an owner financed mortgage of her farm to my sister and her husband. Are there any computer programs that will easily and quickly track all regular and principle payments? We know how to access a simple amortization schedule, but in the event my sister and brother-in-law choose to pay additional on the principal, we want to have a way Mom to easily track this and provide a monthly statement of the principle and interest, just like a regular mortgage lendor would.

Also, any additional advise on what to ensure when entering into an owner financed agreement would be appreciated. We are working with a real estate attorney who has stated that she has created owner-financed mortgage agreements in the past, so hopefully she will include wording that protects all the parties involved.