Must I sit shiva for my sister who is not shomer mitzvos? She grew up in a religious home but now as an adult she says, in effect, it is not convenient for her to be shomer mitzvos. She did not attend religious schooling as a child. She married a Jew who is totally non-shomer mitzvos as well. They know what orthodoxy is all about but may be ignorant of specific halachos. They do know it’s assur, e.g., to travel on Shabbos, but they do any way…same with eating trief, etc.
Thank the Rov.
Although it can be argued that one doesn’t have to sit shiva for a non frum sibling, since they don’t keep the mitzvos, the minhag among the poskim in general is that the siblings should sit shiva. The reason being that nowadays we can’t really know the nisyonos that the person underwent, and we can not say definitively that the person is a choteh to the degree that we wouldn’t it shiva.