I'm sorry you had such a vivid dream......they are disturbing.
IME "counting" on an Ex in an emergency is a crap shoot. Actually, why count on them for anything? Especially one that has moved on to another relationship. Hopefully, you will not experience any kind of emergency.
I don't think it would be in your best interest to go no contact while the house is on the market. I mean, I suppose you could ask the realtor to text you separately. This is a pretty big business transaction so I would stay in the loop. He seems to be cooperative - you need that until the business is over with. You mentioned he is texting you outside of the group texts I believe? If its not anything to do with the house sale just don't engage.
Its hard to move on when you are still in contact. No, I don't think going no contact "avoids" the feelings, it helps not "create" them. I'd much rather deal with a cooperative Ex in situations like this than a jerk - that's really hard. But a cooperative ex brings its own problems......like seeing them in a better light than what the reality is. Statements like "It wasn't that bad all the time"....start a path of forgetting that it WAS really bad, awful.
I am hoping the house sells quickly, and that you can be done with it soon. Other than letting you know someone is viewing the house is there reason for group texts? Sounds like there is more than necessary?