Best way to buy from a family member

My mother has a couple properties she is trying to sell. Her accountant wont let her give them to me. I will buy them at market value which is fine.

Is there a way I can assume her payments without putting any additional money down and retaining the loan? Is that something we would have to work out between us or is there an actual form we can fill out to make it legal and should I even do that?

Any suggestions would be helpful