"Whanau" is a Maori term meaning family. I've talked about this before, but it bears repeating.
Steve is a Kiwi, meaning he is from New Zealand. When we got married, we lived in New Zealand for a number of years, which means I picked up a bunch of the local colloquialisms, or Kiwi-isms. I also got an entire class of preschool kids to use "Dude" in the proper Californian fashion, much to their parents dismay, but that's a story for a different day.
Today's Kiwi-ism is the extremely useful Yeah-Nah/Nah-Yeah combination.
When I was a kid, I would sometimes be asked a question that deserved a positive "yes" response, but was framed in a way that "yes" didn't really make sense.
For example, this morning I had just finished making the coffee and Steve asked, "Did you make the coffee already, or not yet?" As an American, that's kind of hard to answer. Instead of a simple yes or no, you have to fully explain that yes, the coffee is made. It's much easier with yeah-nah.
"Did you make the coffee already, or not yet?"
"Yeah-nah," meaning yeah, I made the coffee, nah it's made. If I hadn't made the coffee yet, I would've said, "Nah-yeah," meaning no, I haven't made the coffee, but yeah I would. If I hadn't made the coffee, and wasn't planning to, it would simply be, "Nah," with a strange up slanted inflection and a pointed look meaning you're making the coffee this morning, dude.
Ok, it's not the best example, but trust me it comes in handy. It's just really hard to explain!
"That movie was good, but it wasn't the best ever."
"Yeah-nah, it was alright." = Yeah, it was good; nah, it wasn't the best ever.
"That cake wasn't very good, was it?"
"Nah-yeah!" No, I disagree with you, it was the absolute best! Mmm...chocolate.
Sorry, I digress.
Now, it should be noted that this is not the American yeah-no/no-yeah. I did a quick Google search, and this is a huge phenomenon in American speech patterns that I was unaware of, but with, apparently, different connotations. From what I can tell, the American yeah-no/no-yeah is just a way of starting a response, sort of like "you know," "like," "so," or even "uh." It's a pause while people's brains fully absorb what's just been said. The Kiwi "yeah-nah/nah-yeah" can be a stand alone answer.
So, next time someone says that the dry tasteless chocolate wasn't very good, huh? You can reply confidently with, "Yeah-nah!"