This article focuses on estrangement between parents and their adult children, while this is an issue between siblings. The only thing I would suggest (and please remember I am not a therapist and this should not be construed as such) is sitting down with your non-estranged children and asking why. Has he emotionally or physically hurt them in the past? Is it jealousy? Those are questions only they can answer and will contribute to your decision whether your son should visit or not. You may also consider having him visit when they are not around. There are simply too many unsaid variables here that may come into play. I believe the best thing you can do is get yourself into therapy and discuss with him/her the reasons for estrangement, the current developments and then follow his/her advice.