Mother in law may have cancer and is refusing a biopsy

Sorry about all the rambling. Stress is really high right now. So as the title reads, my MIL may have cancer and is refusing a biopsy or treatment because she doesn’t believe it. She thinks she will pray it away if she does. Fine, It’s her choice to refuse treatment and i will respect it, but it’s killing my husband. I don’t know how to help him through this. Her doctor wants her to get a biopsy done because she has symptoms such as spotting, pain, weight loss, and she always feels sick. She’s 63 btw. She is also being manipulated by my brother in law who is a paranoid schizophrenic and told her that God told him that she will go to hell if she gets cancer treatment and she believes him. She if refusing to believe his diagnosis and truly believes he is a prophet. She and my brother in law are in a cult that my husband ran away from years ago. I don’t know how to help my husband at all. I know if it were my mom, I wouldn’t accept this refusal of treatment, but on the outside looking in, I know she will never give into it, and it’ll only make things worse for him to not accept her choices.She’s getting worse and her mind is not the same. Her memory is failing her, and she is walking very slowly and mentally regressing into a child. I promised my husband we will spend Thanksgiving and Christmas with her this year in case this is her last. As much as I can’t stand her, I owe him this.