There is discussion here about saying Kaddish for parents and also some discussion on Kaddish for a sister. One place on the Chabad website states that Kaddish should be said for 30 days for a sibling while another place also on the Chabad website (see comments below article) states that 11 months is customary.
For how long is Kaddish said for other relatives? What sources back different traditions?
I am specifically concerned about the case of a deceased sibling, but I am also curious about minhag for Kaddish for other close relatives such as children.