The grandchildren lose more. They come into a family that is split and so are their brains: one side is what they see and the other side is unknown whether there is truth or lies. There will always be something missing from these grandchildren's lives and their psyche is not intact. It can turn them into perpetual liars or non-committal people.
Also: when there is a MIL problem, there is the eternal triangle--wife, husband, MIL. I have these troubles with my son and as far as I am concerned, I cannot get OUT of their marriage inspite of the fact that they never respond to any contact from me including no responses to gifts sent to the grandchildren.
I took my son to a therapist with myself in the beginning of the schism and the first thing she said was: Well, what are you going to tell the children????
There was no answer. A month later my son lied to the therapist about whether he had or had not notified me of his cancellation of a scheduled visit.
No one who knew my relationship with my son can even believe that this has happened because it always seemed he loved me. Well, we MIL have to make our peace and preserve our mental health and for me this demands that I not have contact with sadistic and deceptive blood relatives.
Sue