Hello Titm: Thank you for bringing your concern here to PC.
Welcome to Psych Central.
I'm sorry I don't think there is a lot I can offer with regard to your concern. (Hopefully there will be other PC members who will have some thoughts they can share.)
Personally I'm with the people who've told you this isn't your fight. You're being repeatedly drawn into a battle you have no way of resolving. Your mother & your sisters have to resolve their differences themselves. And if they cannot you can't make that happen. It's sad your mother may have cancer. But you still can't change what is happening between your mother & your sisters.
Basically what's occurring here, it seems to me, is that you are being manipulated by your mother who's using you to satisfy her own emotional needs. What may be necessary, it seems to me, is simply for you to establish & enforce some personal boundaries. (I say "simply"... I know it's not really that simple.) I realize that's not easy when it's your mom. But the alternative may well be to just be continually drawn back into this no-win dispute.
Here are links to 10 articles, from Psych Central's archives, that (hopefully) may be of some help with putting the situation you're in into perspective. The first 3 links are to articles on the subject of manipulation. The next 4 links are to articles on the subject of personal boundaries. Then come links to 2 articles on enmeshed relationships. And finally there's a link to an article on how to deal with difficult family members:
How to Spot Manipulation
5 Warning Signs of Manipulation in Relationships
Tactics Manipulators Use to Win and Confuse You
What Are Personal Boundaries? How Do I Get Some?
What Are Healthy Boundaries and Why Do I Need Them? | Happily Imperfect
https://blogs.psychcentral.com/imper...hy-boundaries/
https://blogs.psychcentral.com/imper...dium=popular17
https://blogs.psychcentral.com/imper...dium=popular17
https://psychcentral.com/lib/tips-on...dium=popular17
https://psychcentral.com/blog/how-to...amily-members/
I hope you find PC to be of benefit.
