Wow. With that many people "supporting" her, you should encourage her to follow her own gut instincts. Thankfully, we didn't go through this very much (although it was touch and go with 2 of my 4 siblings for awhile when they remained in denial about mom's condition), but some family friends did when the 4 adult kids, mom & mom's relatives had some disagreements about "what was best" for the dad who was dying of kidney disease/renal failure.

Only one person should be making the decisions as surrogate, and that is your sister, in consultation with the doctors, her minister, and maybe one other trusted person.

Not everyone in the family will agree with her decisions much less support them, but she is the one who has to live with them the rest of HER life. Support her that way, is my advice. That is one thing that someone at a distance can do, when there is a potential (especially with adult children) conflict or potential interference by well intentioned family and friends trying to influence your sister's decision making for her husband. That can be really tough.