select_siblings.py

# https://blenderartists.org/t/how-to-select-bone-child-objects-in-one-click/660780/16

bl_info = {
    "name": "Select Siblings",
    "author": "Stanislav Blinov",
    "version": (1, 0, 0),
    "blender": (3, 0, 0),
    "description": "Select siblings in object mode (respecting distinct bone parents)",
    "category": "Object",
}

import bpy

class OBJECT_OT_select_siblings_deep(bpy.types.Operator):
    bl_idname = "object.select_siblings_deep"
    bl_label = "Select Siblings (Deep)"
    bl_options = {'REGISTER', 'UNDO'}
    
    extend = bpy.props.BoolProperty(
        name="Extend",
        description="Extend selection instead of deselecting everything first",
        default=False)
    
    @classmethod
    def poll(cls, context):
        return context.mode == 'OBJECT' and context.object
    
    def execute(self, context):
        ao = bpy.context.selected_objects[0]

        for o in bpy.context.selectable_objects:
            if o.parent == ao.parent:
                if (o.parent_type != 'BONE') or (o.parent_bone == ao.parent_bone):
                    o.select_set(True)

        return {'FINISHED'}
    
def register():
    bpy.utils.register_class(OBJECT_OT_select_siblings_deep)
    
def unregister():
    bpy.utils.unregister_class(OBJECT_OT_select_siblings_deep)