One of the things that came up a couple times is reading the furniture as a sign that this is for the long haul. I'd say that you should expect that it is for the long haul, as it never goes as fast as we think it should, but the furniture isn't a sign that she is at the point of no return.
No matter what, she's likely not staying in her sister's place for the long haul. It is just a temporary stop over. Yet, she dragged all that stuff over there. She isn't thinking things through. Matt's post on WAWs explains why they aren't thinking things through with the big picture or perspective in mind, acting impulsively, making decisions based largely on emotions, etc. The furniture is just part of this.
On the showing no signs, what signs are you expecting? What are your babysteps that you are looking for? Don't expect a quick turn around to "I'm sorry, I made a mistake and I want to work to save our M," or "I've been thinking I was a bit rash and would like to talk." Frankly, that kind of honest, self-reflective apology may never be forthecoming, but even something that is a clear sign will likely take a lot longer than you are expecting even if you double or tripple or quintuple your expectations. That's why MWD says you need those babystep goals to look for.
Don't worry about how f*ed up her sisters are. There are likely some family of origin issues that your W will need to deal with in IC (something you might think about asking her to do as a later part of reconciliation if you get to that point, so that you build an M that is less likely to go this way again). Her sisters' Hs almost certainly didn't handle it the way you are. They almost certainly lacked the tools you have (DBing, the forum, etc.). Were they the types to stand up in their sitch, make the hard changes, take responsibility for their kids, and give their Ws the space to work through their sh*t? I strongly suspect there will be a lot of no answers if you look at it.
We all feel at times like throwing in the towel, getting off the ride because it is hopeless. Will that be good for your S? Will life get any easier? You'll still be dealing w/ her for a long time to come given the kid. Is it that you really are hurting and missing the companionship of a W? Is it that you wish to move on and have other Rs to give your the soothing and comfort you are missing? If so, that's a band aid that will not solve the problems. It [censored]. It really [censored] at times. We all feel hopeless at times. It does pass. I don't see any recent changes that suggest you are at the point of giving up unless you have decided that it is not worth pursuing. Only you can make that call.
Maybe focus a bit more on what you are doing for GAL. You clearly have your S a lot, and that and worrying about the M is very emotionally draining. We need some things to fill the tank from time to time. A bit of time away. Something that brings us personal fulfilment (a hobby or place or people) to rejuvenate. Single parenting is really, really tough. Are you getting the time you need away? What would it take to get that?
Good luck!
Me: 50 W:43 S6, S3 M: 12 yrs. T: 17 M is bad & Not happy Bomb Mar '14 S 5 Feb '15 D Bomb 13 Apr '15 (but "no hurry") DB Coach May '15 Wants proceed on D Aug '15 Starting 1-on-1 negotiations Sept '15