My heart goes out to everyone in this thread who has been hurt by family, whether by siblings, ils, ac or whoever.
Maidmarion, I think it's slightly different for you that some other members because you haven't been estranged from your daughter as long - some of them have been going through this for several years, you're only speaking of months. It seems to me that means there's more of a chance that the situation will thaw out.
Vonnie, is it possible ds' dad has asked him to end or lower his contact with you? Be that as it may, I'm glad the 2 older gc keep in touch with you. Maybe the youngest one will reach out to you when they're older, too.
IMO, you make a great point, Eloethan - there's a difference between whether siblings socialize together or support each other. Wonderful if they can do both, but it's not always the case. However, not socializing doesn't mean they won't defend each other, and the second, I feel is the more important of the two.