contract for deed advice needed asap

[Victoria Monroe]

My mom and her husband of ten yrs had been buying the duplex she had lived in for the past 44 yrs, contract for deed.  he passed away 4 yrs ago (without a will) and she continued paying the bills.  (she had more money than he ever did anyway and had always paid the biggest part of any bills due).  she passed away suddenly 2 months ago and her will states she left everything to me her only child.  she had a verbal agreement with her landlord that if anything every happened to her before the contract was paid off that i could finish paying for the duplex.  the seller and i asked the title company to make up a new agreement between them and me so i can finish paying the duplex off (only has 2 1/2 yrs left to pay).  well they need to do some investigations and make sure i am her only child - no problem, since i know i am.  but since dons name is still on the contract the title companys lawyer needs to know if he had any children, their names, addresses etc so he can send them paperwork to sign and have noterized stating they relinquish any rights to the property.  
my question is:  had there been no verbal agreement between my mom and the sellers, wouldnt the property have just gone directly back in possession of the seller?  and since the verbal agreement between my mom and the seller was only about me paying off the house, why would my step=dads children have any rights to it at all?  btw they live in different states and have not contacted my mom about wanting anything over the past 4 yrs.