We are a commune of inquiring, skeptical, politically centrist, capitalist, anglophile, traditionalist New England Yankee humans, humanoids, and animals with many interests beyond and above politics. Each of us has had a high-school education (or GED), but all had ADD so didn't pay attention very well, especially the dogs. Each one of us does "try my best to be just like I am," and none of us enjoys working for others, including for Maggie, from whom we receive neither a nickel nor a dime. Freedom from nags, cranks, government, do-gooders, control-freaks and idiots is all that we ask for.
If you can match notes, I could teach you to do that. Learning the odd intervals would take a while, but most of it becomes natural once you learn to "hear" the major thirds and land on them instinctively. CSN (&Y) seldom strayed far from those parallel harmonies, so that would be a place to practice humming along.
Assistant VIllage Idiot
Want to hear good harmony?
Try the Everly Brothers or the Beach Boys.
My neighbors and I sing and play together for local events. "If I Fell" is one of our favorites. The Beatles and the Everly Brothers are an inexhaustible supply of terrific harmonies. It doesn't great enormous skill, you know -- just practice. With a little more practice, you can ad lib a third part to any standard two-part harmony, as bluegrass bands and folk musicians of all stripes have been doing for ages.
If you can sing at all you can do that. It's all about practice and training the ear. It would take some time if you've never done it before, that's true. I've been lucky enough to sing in my church choir for a choirmaster who is also a M.A. in piano performance and does vocal coaching for $$ for aspiring opera singers. What I get for free would cost me $60/hour if I hire him privately (as I have on a few occasions).
Does he go to church? In all seriousness tell him to join the choir. That'll give him the training his ear needs to pick out intervals and chords.