"Yeah nah yeah" is a phrase that confuses the fuck out of tourists, because it means both yes and no, depending on where the emphasis is.
'Yeah nah yeah' means yes, and 'yeah nah yeah' means no.
'Chur' is 'thank you'. The North has a lot of Maori influence so you get stuff like
Haere mai: literally "come here" but it's a general way of getting attention.
ka pai: well done! awesome!
You won't often hear fluent 100% Maori in public but you'll often get it mixed in with English -- a common phrase is "haere mai, time for kai!"
'Sweet' means 'good'', and we use 'as' as an exclamation mark. Putting it all together: "Bro come over for kai." "Yeah nah yeah, sweet as, bro"