In terms of saying devarim shebikdusha in front of an uncovered part of a womans body (arms, etc) is there any difference if it’s a Father and the woman is his daughter or if it’s a brother and his sister?
Answer:
The halachah of not saying devarim shebikdusha (berachos and so on) in front of immodestly dressed women applies even to a daugher and a sister.
The Biur Halachah (75 s.v. tefach) writes that for a daughter one can be lenient up to the age of eleven, and this ruling can be applied to a sister, too.
