Possible Quiet Title Action

My father died intestate in 2004. He has 5 surviving children. Our stepmother survived him. This past year our stepmother contacted us through her attorney. She and our father met in 1989 because she was to buy his house. They began having an affair and married. According to her as part of the sale our father received a promissory note calling for payment of $17,000 over five years and secured by a second deed of trust on the property. Since they married our father told her she no longer had to make payments on the note but he never recorded a reconveyance of the deed of trust. Our stepmother now wants to refinance her home but cannot due to the lien which remains. Her attorney sent us a Small Estate Affidavit and Substitution of Trustee by Beneficiaries to sign. She would hold 50% in the promissory note and each sibling would hold 10%. She would be substituted as new trustee.
There is a great deal of animosity between our stepmother and us as well as between us siblings. She is threatening a lawsuit if we do not sign the papers. What are our options? If she files a lawsuit can we disclaim any interest and be rid of this issue?

You need not sign--and she will have to prove her case! She may actually not want to even try to do so.