Is a person's discussion with a relative (such as a mother with her son about her other son, or a wife with her husband about her brother, or one brother to another about their third brother) considered backbiting?

Backbiting has been condemned by the Divine Law, and it is defined as mentioning your brother with something he dislikes. However, it is not backbiting if your mention of your brother in his absence is for a legitimate purpose, such as offering advice, or seeking assistance from someone capable of rectifying a mistake or changing an evil, or complaining and seeking help, or inquiring and seeking a fatwa (definition), or warning Muslims of evil, or if the person is openly committing فسق (immorality) or bid‘ah (innovation), or for the purpose of identification.