The Grand Duke and The Grand Duchess will attend the wedding of Prince William of Wales and Catherine Middleton.
The Cour Grand-Ducale confirmed their attendance at the request of Luxemburger Wort. The Cour did not release any further details. Wort noted that they did not provide details of any additional members of The Family attending. Given the scope of the invitations to the other royal houses, I wouldn't really expect anyone other than Henri and Maria Teresa.
Source: Luxemburger Wort