The actions of the adult child today are not a reflection of the parent yesterday. We as adults are 100% responsible for own own actions & life, for our own choices and decisions. So let go of the attachment to blame others for what we do.
People use use children as weapons to hurt others are emotionally immature. The only valid and legitimate reason for any kind of alienation is if the person is being abusive to the child or the childs life is being endangered. Any sort of anger or disagreement between adults NEVER excuses child alienation, whether it be with the other parent, grandparents or other relatives. Keeping a child from those who love the child is a huge disservice to the child.