I am deeply wounded by some of members from by biological family.I did what ever I can.Eventually realised it is impossible to please toxic people.For my own sanity I started keeping distance.Some wanted me in the picture again,but I refused and stood my ground.I don't want to involve in their toxicity. I have had enough.I advise you not to be the middle man.Let your sister's handle their relationship with your mother in this health crisis.You decide how you want to handle yours. All the best.