Go check out Bethany and Joe, they have three albums out now (all short) of fantastic bluegrass versions of Christmas songs (mostly carols)
pastemagazine.com/noisetrade/m...-the-king

bluegrasstoday.com/heaven-and-...-and-joe/

bethanyandjoe.bandcamp.com/

pastemagazine.com/noisetrade/m...-emmanuel

There, there's links to all of it. The instrumentation is all outstanding, and the mandolin really stands out, these folks are great! Well worth a listen, and if you like it a donation is also recommended (but not required)
Also the Purple Hulls have a fairly new Christmas album that's really good
thepurplehulls.com/