Rely on her wishy washiness to comfort yourself. You know from personal experience how hard it is to move, kind of doubt she'll go through all that trouble and if you make it a little inconvenient for her (low profile :-) she may decide it doesn't look as convenient. Be the horse you can lead to water but not make drink; drop the ball a few times with stuff you're supposed to do, etc. Let the sibs assume whatever they want about whose turn it is to take care of mom, just don't respond/help do it very enthusiastically and it might fall through without too much upset on your part.

Don't get ahead of yourself either in the stress department, imagining what it would be like :-) She isn't there yet.