You bet there is. One of the best sibling recordings I have is from the Rex Humbard Family (yup, the faith-healin' tv evangelist) singing "I'LL FLY AWAY". It's so tight you literally don't know who's singing which part. The Louvin's were amazingly tight, but for sheer excitement, the best I ever heard was Alton and Rabon Delmore sing "I Got the Kansas City Blues".....may have been the first song they recorded and they were on fire!

Cheers

Rick