What a difficult situation, and how insightful you are.
Your family is right that you can't change her, and I think that you understand that change can only come when she wants it to.
What you can do that is different than what your family is doing now is move out of denial and openly acknowledge to others and with her that her alcohol abuse is having affects on you.
Setting boundaries is very important, and you have started that by telling her a year ago that her drinking hurts you and you don't want to be around her when she drinks. Maybe you can have another discussion with her - when she is sober - and when you have thought through what boundaries you want to have and are ready to enforce them.
Alanon may be very for you and your fiance, especially since his grandfather is an alcoholic. There are damaged patterns of parenting in both your families, and it might be very constructive for you both to do some sorting out of that before you have children so that alcoholic behavior is not part of their legacy.
This forum is a great place to come, and I am sure many will offer you more wisdom than I can. Come back often,
BothSidesNow