I empathise with everyone dealing with the fallout from family/estrangement issues.
It is often something I have thought abut posting on, or more accurately, venting on, here, as it certainly contributes to my anxiety/stress. It is also somewhat of a taboo area though, as there is a large element of shame and embarrassment associated with this.
My family is an absolute mess in this regard, unfortunately.
Not to go into a lot of detail but I have only ever seen my father on a handful of occasions, and of 3 siblings, I am estranged from two, an older brother and older sister. Brother for 5 years and sister about half that time. No contact at all, well almost none.
I think in general terms and having read quite a bit about it, a lot of sibling estangement is seemingly the replay of unresolved issues from childhood. I also remember listening to a documentary about estrangement on R4 where one lady spoke of being completely cut-off by her son for no apparent reason. She made the point that his father had also vanished abruptly many years previously and that as she saw it, estrangement is learned behaviour. There is a lot in that too I think.
I have suspicions particularly relating to my brother, as he divorced, remarried, and became a father for the first time all in a very quick timeframe, that his new wife may be maintaining the estrangement to a large degree. I texted him out of the blue a few months ago, asking if he would like to meet up, and got an encouraging reply. But alas, I spent the next few weeks suggesting various times and places we might meet, but he found a reason to reject them all, and the contact just petered out.
It is my mother I feel sorry for as she is in her mid-70s and cut-off from contact with her oldest son and daughter too. It is tragic for her, very hurtful and upsetting seeing birthday and Christmas messages and the like persistently ignored over several years.
Look after yourselves all.