"Nadw" should also be correct here, once again, ignoring the fact that people in the north say things differently.
But this is for the South Wales dialect.
You can tell because of the pronunciation of 'u'.
The point is that both the South Walian and North Walian dialects should be accepted. I'm not sure what you're on about with regards to the "u", I assume the fact that "eisiau" isn't "isho" as it would be written and said verbally.
In North Wales 'u' is pronounced as a close central unrounded vowel (ɨ) and in the South it is a close front unrounded vowel (i).
is there a reason why this isn't dw i'n eisiau ?