The Umm al Qiwain overprints are: 5 NP on the 1 d value, 10 NP on the 1 1/2 d value, 15 NP on the 2 d value and 20 NP on the 3 d value. Note: the spelling is UMM AL QAIWAIN.
I will add more information about these stamps as I find it.
My thanks to Khalid Al Omaira for supplying me with the images of these stamps.