Query to fetch missing siblings [closed]

Question

        DECLARE @AName        VARCHAR(100)
        DECLARE @BName        VARCHAR(100)
        DECLARE @CName        VARCHAR(100)

        SET @AName            = ''
        SET @BName            = ''
        SET @CName            = ''

        SELECT
            ChildsChildId,
            ChildsChildName,
            ParentsChildId,
            ParentsChildName,
            ParentId,
            ParentName
        FROM
            (
                SELECT
                        ''                        AS 'ChildsChildId',
                        ''                        AS 'ChildsChildName',
                        b.Id                    AS 'ParentsChildId',
                        b.[Name]                AS 'ParentsChildName',
                        p.Id                    AS 'ParentId',
                        p.[Name]                AS 'ParentName'
                FROM [sch].[ParentsChild] b
                    INNER JOIN [sch].[Parent] a
                            ON a.Id = b.Id
                WHERE NOT EXISTS
                (
                    SELECT *
                        FROM [sch].[ChildsChild] c
                        WHERE b.Id = c.Id
                          AND c.Id IS NOT NULL
                          AND c.Active = 1
                )
                AND b.Active = 1
                AND a.Active = 1

            UNION

                SELECT
                        c.Id        AS 'ChildsChildId',
                        c.[Name]    AS 'ChildsChildName',
                        b.Id        AS 'ParentsChildId',
                        b.[Name]    AS 'ParentsChildName',
                        a.Id        AS 'ParentId',
                        a.[Name]    AS 'ParentName'
                FROM    [sch].[ChildsChild] c RIGHT JOIN [sch].[ParentsChild] b
                    ON b.Id = c.Id
                        INNER JOIN [sch].[Parent] a
                    ON a.Id = b.Id
                WHERE    a.Active = 1
                        AND b.Active = 1
                        AND c.Active = 1

        ) a
        WHERE        (a.ParentName            = @AName    OR ISNULL(@AName, '') = '')
                AND    (a.ParentsChildName        = @BName    OR ISNULL(@BName, '') = '')
                AND (a.ChildsChildName        = @CName    OR ISNULL(@CName, '') = '')

I've this above query where I need to fetch all the records from the three tables. First table [sch].[Parent] has a field referenced as Foreign Key in second table [sch].[ParentsChild]. There are records which are in both the tables with their FK. Now, there is a third table [sch].[ChildsChild] which is also referenced by FK of second table [sch].[ParentsChild] table, but there are records missing for the entries in second table. So now I need to fetch all the records from three tables including JOINS for all three tables and for those also whose records are missing from third table i.e. [sch].[ChildsChild] table. I've the query, but need to know if there is any other more COST effective query than the above one.