I have 2 co-signers on my house what rights do they have?

I bought a house in the late 70's at the time I need a co signer so I got my mother and my sister to do it for me. My mother helped me with coming up with money for everything and my sister helped with nothing. My mother now lives in the house for the past 28 yrs. My problem is that my sister is waiting or wanting my mother to die so that she can get the house and let her adult children stay there.I would like for her to get a reverse mortgage.I no longer want anything to do with the house since I left thereafter getting married. So i would like to know what rights do cosigners have. Does she have the right to do what ever she wants when my mother dies. My mother plans to will her part to my brother which is good my brother is who helps her with all her bills connected to the house PLease give me some advice on what to do with this problem. This is bothering me and bothering my mother even more that her daughter is only thinking about what she is going to get once she is gone.