Estrangements happen for a variety of reasons, there's no one size fits all.
Sometimes it can be due to the poor behaviour of EPs, past or current, and sometimes it can be down to the poor behaviour of the ACs.
Everyone has their own experiences, and every single one will be different.
We all have our own recollections of childhood, good, bad or indifferent. Between siblings, recollections can vary.
Some, as adults, after a poor childhood, choose to estrange. Others choose to put it behind them and move on.
My two stepsons are estranged now from DH (and me) - one because we won't find his alcohol/gambling addictions, and one because "he doesn't want the burden of elderly parents". I was a bit bemused by the "burden idea" as neither of us have ever asked for a thing...🤔. We have helped them far more, over the last 20 years,
But, fair enough I suppose - but as neither DH or I are willing to do the "eggshell walk" with them, and pander or plead, they will just have to get on with it.🙄
We've got a full life anyway, and although I think that one day, his sons will regret their behaviour, as DH is in poor health, that will be their problem.
However, what I won't accept is that this is in anyway down to us. It's not.
Telling EPs that they must know, hold responsibility for and understand the reasons and justification for their estrangement is unfair and a bit arrogant. Outsiders cannot possibly know.😗
Sometimes the EPs are at fault, sometimes the ACs are, sometimes in in-laws are, and sometimes all sides have handled things badly.
There is also the point that some estrangements are caused by mental health issues. No one's fault - just the way it is.