Attributes are defined on the ItemCategories and those can be nested with multiple parents. That means a Category can have both multiple parenst and multiple children.
So sometimes you can have multiple parent categories with the same attribute.
Remove from parents will just remove the attributes from any parent category while keeping the attributes on children categories
Remove from all Relevant Familly will remove from all parents and all childen of this category
Remove from All Familly will remove from all parents and all children of those parents
I hope that makes sense. I general it is better to organise your categories in such a way that attributes don't have multiple roots (but it some cases allowing it does simplify things that's why we don't prevent it)