Should I pay off my grandma's house?

i recently found out my grandma's house that bought in 1965 for $6000 has an unpaid balance of $7000 because my mom has not paid off the second mortgage her and my dad took out on grandma's house in 1990.
according to my grandma's will dated 1989, the house was paid off and was to be left to my dad when she passed but in 1990 my parents asked to mortgage grandma's house to help them purchase a vehicle for their business and they would make mortgage payments and my grandma said yes. in 2003, my dad died which left my mom making grandma's house payments and mom has been struggling financially ever since dad's passing and the house still has not been paid.
i am now my grandma's caretaker and have moved in with her because she is 92yrs old. she is in good health but without me would be alone. i am trying to get my grandma's financial and legal matters organized and prepared and i have made an appointment to update her will but i am thinking should i pay off my grandma's house and have her sign it over to me? because it was already willed to my dad it will be left to my mom and grandma told us "grand kids" the house would be ours when she passes. i feel i have to hide what i am doing from my mom because she has her own plans for grandma's house. but if i'm her caretaker i shouldn't have to hide anything i am doing.

please help!!