Yosef Karo

“ And there are those who say that nowadays, the practice is to be lenient in this mourning with those for whom one would mourn, because this is only for the honor of the mourners, and nowadays all of them relinquish their honor. And thus the practice nowadays is not to mourn at all with those for whom one would mourn, and all who are strict with regard to this are considered shocking. But in any event, the practice is that all the relatives of the dead person who are forbidden to him as witnesses indicate a little of mourning themselves for all of the first week. ”

“ All the relatives for whom a kohen must become impure – his father, his mother, his son, his daughter, his brother and his virgin sister through his father, and his wife – one mourns them. They [i.e. the sages] further added to them – his brother from his mother, his sister from his mother whether a virgin or married and his married sister through his father – one mourns for them, even though a kohen may not become impure for them. ”