They're a horrible DC-area band named Sev. Their album, "All These Dreams", got released a while ago and bombed hard. This is the THIRD mix of their single, "Same Old Song", and it just ALMOST charted last time, but still...three times it bombed? Pretty pathetic. Yep.
Not quite carolers, but some rather more trad-ified versions: Irish Tenors (phobos.apple.com) Ronan Tynan (phobos.apple.com) Youtube of the song done on accordion (youtube.com) BTW, its my favorite Xmas song too.