Igros Moshe EH 4:64-3 seems, without explanation, to permit yichud with a woman and her daughter or granddaughter. If this is truly Harav Feinstein’s view [it may very well be that this is a printing error], it is contrary to the view of all other poskim and is against the basic principles of hilchos yichud. Please clarify.
It says explicitly in the Gemorah Kiddushin 90b that there is an issur yichud one man with two women. One man with many women (at least three women) is a dispute amongst the Rishonim. The Rambam and Tosfos hold that with many women is also ossur and so paskens the Mechaber, but Rashi holds that yichud is permitted with many women quoted by the Ramo. The gemorah in Kidusshin 81b brought in E:H 22:10 says that if the woman is with a small child there is no issur yichud. I would like to suggest that a word has been omitted in the Igros Moshe i.e. “ketanah” and should read: אם אמה ובתה הקטנה וכו’ ובת בתה הקטנה וכו.