I heard it’s a machlokes if a brother and sister are allowed to touch one another (a friendly hug or kiss on the cheek). Please will you provide the different opinions on the matter? Kol tov!
The Shulchan Aruch quotes the Rambam regarding this “A person who kisses or hugs a blood relative, even if it from those relatives that a person heart doesn’t have desire for them, such as an adult sister, etc. even though he isn’t deriving pleasure from it, it is exceedingly disgusting, a prohibited thing, and the act of foolishness”. It is clear from his terminology that he is not saying that it is permitted, the question though is does he mean to say that it is just disgusting, and we are to distance ourselves from it, or it is an outright prohibition. The controversy stems from the fact that he says that it is disgusting and “issur” does he only mean that we shouldn’t do it because it is disgusting, or an actual issur. The Bach (Kuntres Acharon-5 on the Tur) says that according to the Rambam it is not a prohibition if the person doesn’t derive any pleasure from it, however if he derives any pleasure from it, then it is a biblically prohibited. See sources.
Hilchos Issurei Biah 21-6,7, Tur Even Haezer 21-7, Shulchan Aruch ibid, Prisha ibid 6, Otzar Haposkim E:H 21-51. See Igros Moshe E:H 4-63 that although it is not permitted, it is not on the same level as other forbidden women, rather a lower level prohibition so that we should not get accustomed to doing thing like this with other women. Also see Imrei Chaim Pinchos- Nidda pg. 143-17, Chut Shani E:H pg. 64 who understands the Rambam that it is not outright prohibition, rather that it is from the things that we should not do. In extenuating circumstances, one should consult his Rov.