Sibs as well as parents have a choice. Should they worry about what other people think or do they need to worry about what this unfortunate OTD child thinks. What does Hashem want from them, to worry about your neighbors and yentas or to worry about the people nearest and dearest to you who needs you to love them and care about them when they are in the worst distress of their lives?
Who should you have loyalty to? Please, honestly think about it. If you stop worrying about what the world thinks about your sibling and understand that we each go through our own nisayon and Hashem will judge us on how we each deal with our challenge then we can handle this better. The OTD child is going through a nisayon of his/her own. The parents and siblings are going through another nisayon, how will they handle this situation and how will they treat this child, Hashem’s child, who is going through this terrible rough patch and journey in his/her life?