Hi Titm, welcome to Psych Central. I'm new here as well. I'm sorry that you have to deal with this and be stuck in the middle, and that your mother may have cancer. I agree with Skeezyks, and I've got nearly 40 years of dealing with a manipulative parent. I am so sorry; as I know what it feels like to feel so torn.

Unfortunately, you may have to just very clearly tell her that you've tried repeatedly to speak to them and at this time they aren't willing to speak about this. It may be helpful to tell her that maybe giving them some more time (Not a day, or a week, but maybe some months...) would help heal the wounds that are clearly deep and allow some sort of communication between them at some point in the future.

If she won't agree to that, you may have to create some boundaries regarding your mother and stick firmly to them. For instance, I used to tell my mother that if she wanted me in her life, she needed to stay sober (she was an alcoholic and was a very abusive drunk). My mother got sober, and remained sober for the last 7 years of her life(with one brief slip) as a result. I'm not saying that this will work like magic and she'll quit drinking and manipulating you, but it may help if you set and enforce your boundaries with her.

I hope that this helps, and I hope that you feel better!