I think the key thing is there. And thus I guess I need to repoint out again; Is she "really" asking you for advice on how to deal with this, and the intention (by her) is "by any means necessary", and "no limit on what she needs to do to make this happen" because she's ready to take action over this? Or is this you (the family) interpreting this as what she wants from you (her family) to do for her and she actually only wanted to vent to someone she can do to instead? And actually has ZERO intention of doing anything?
In some cases, "some" people (like those on how you're describing her), just need to vent, and have absolutely no problems at all really with the poor hand they have been dealt with to play. Because given what you have written there that I have quoted and highlighted, there's a real danger that might be what they're doing, and you might be overstepping through misunderstanding their actual need.
Note, I'm not saying it's not a bad situation to be in, only that as someone (you; the family) who does care for them, and that description of them from you, that you aren't ending up treading on something else in the end (her self esteem) that you might not be able to untread from (and make things a lot worse). Have you talked to her and explained to them that it might be necessary to talk the "ultimate" step to get what she wants, and that means Divorce? Because if she's not down with that, there's nothing more to really say or do at that point.
Your most recent post tells us she's gone to sort her Will out and that she's asked about Divorce and what would be split; that only tells us that she's done this, maybe in hopes in being able to use it as a bargaining chip to get what they want (which may not be actual Divorce). But is she able to take this final step however? Given your description of her?
Again, I'm sorry if it sounds like I'm repeat, just I'm quite aware of how fragile some peoples minds can be, and just want to be sure you're all on the same page before something is done that only sends her into a worse state and spiral that they may not be able to get themselves out of.