Game concept
Extended Family
The game also links it as Extended Family Members.
From the game's encyclopedia
The Extended Family of a character includes:
• Cousins
• Uncles
• Aunts
• Nephews
• Nieces
The game's text for patch 1.20.1.2. Words in blue are entries of the encyclopedia: hover one to read it, as in the game.
Extended Family is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "The Extended Family of a character includes:" It is part of Family. The game also links it as Extended Family Members. Patch 1.20.1.2, from game/common/game_concepts/00_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/00_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.