The Pischei Teshuva (Hilchos Yichud EE Siman 22 sif-katan 2) brings that yichud with a father and daughter together with another woman is ossur. What is the halacha l’maseh in such a case? As well what would be the case if you have a Father and many daughters (let’s say 3) together with another girl not from the family all sleeping in the same house (obviously the father in one room and the girl together with at least one of the daughters in a different room.)
(From what the P”T brings at the end over there could be a reason to say why it should be ossur even if there are many daughters and a father together with another girl.)
Answer:
Although the Pischei Teshuvah cites from the Zechor Le-Avraham that this is prohibited, Rav Moshe Feinstein (Even Ha-Ezer 2:15) notes that this is very difficult (from se’if 5 in the Shulchan Aruch), and although he tries to explain the stringency, his conclusion is that the situation is permitted.
This is also the agreement of other contemporary poskim (see Nitei Gavriel 27:4; Devar Halachah 8:4; Igros Moshe ibid., and Even Ha-Ezer Vol. 4:65:8; Toras Ha-Yichud 8:3).
