WOW, maybe the more appropriate way of answering that question is “my brother is in a lot of pain, thank you for asking about him, we are all very concerned for him, he is really suffering. He is going through a tremendous nisayon and we are lucky that he made a connection with Rabbi ….. we truly hope that he will be able to help him and he will be the right sheliach for him. It hurts so much to see your own sibling have a yeridah and know that there is nothing you can do but daven and learn for him and his refuah, we are all doing the best we can”
By answering in this fashion, one takes the bull by the horns and shows that they are NOT ashamed of their sibling, and they are NOT at risk of following him down that path therefor there is no risk in taking the child into the yeshiva.