Yep, they're Canadians from Mabou, Cape Breton.
One thing you gotta understand about voices too - you don't get to choose your range. It is a natural consequence of the shape and size of your vocal apparatus. I could barely growl out middle c when I was 20, and I still don't like to go below the under that at the ripe old age of 33! And I can still sing notes that aren't on the harpsichord, they're so high (when my voice is in shape). With women, the chords nearly always follow the body type. I'm a wee little 5', 95# woman. I ain't never gonna sound like Dolores Keane (but I can dream....).
As far as sounding nasal, well, Gaelic, at least the Irish/Scottish/Manx branch, is a nasal language. If you pronounce a word like the name Dòmhnaill, the mh is right up your nose!
I betcha they'll grow on you over time, if you think about all that while you're listening to them. You'll like Cookie Rankin best - she's got the best, most mellow voice, and she typically does the low harmonies when the lot of them sing together.
Tiaridh,
ciarili