Sorry to give my opinion - or even better, ask for advice -, but maybe I can help, even if it is just a little bit. I understand both parts, Meloni. My mum has lung cancer and I really live far from her. We literally have an ocean between us, as she lives in Brazil and I live in Spain.
As I knew what was going on, I left everything to be with her (my husband, my job, my house). My first thought was to help and take care of her, being a support for her and my father... I'm seriously thinking to stay with her until she is well again, no matter how long it lasts. She is not only my mum, she is my best friend. It is really hard to feel that I have no control on this situation, that there's nothing I can do to really stop this cancer. My heart only wants to return all love and confidence she gave me. But many times all I can do is be by her side in silence with my daughter in my arms.
By the other hand, I understand that sometimes she is overflowed, tired, sad, angry; wanting to be alone. Despite respecting her space and the right to be alone, my heart cries "run to her and hold her hand".
I don't know your family, but I think that they, as me, only want to help and don't know how. Whatever it is, love forgive all.