Huw can not only sing, he can also play the harp. (Small harp that one holds on one's lap, not a concert one!) What is more, I know exactly what his singing voice is like. I heard a voice once on the radio and thought, "That could be Huw singing!". I rushed out to buy the CD. *g*
Elen can sing perfectly well enough for all social and religious purposes, but was too much of tomboy to want to learn to play an instrument, even though her parents hired a teacher for her. Siarl can sing well, as can his bodyguards. I have no idea whether they were selected for their musical ability or whether that is a pure coincidence. It does, however, come in useful near the end of A Legacy of War. Cai the groom doesn't seem to sing, but he whistles tunefully. Madlen the maid has a very pretty voice, which is mentioned near the beginning of the book.
With regard to the current WIP, Mark is not a singer, but can hold a tune adequately if required to do so, in church, for example. This applies to most of the other Light Cavalry troopers too. They'll chant in the temple or sing in church; they'll sing whilst performing their ablutions in the wash house and sing dirty songs when drunk or around the campfire, but if you asked them to sing solo on a stage, they would run a mile.
The king and prince, also people like Lord Angrak, will have had a least a little musical education. The ordinary people will have picked up folk songs, or popular ditties from the song and supper clubs, by ear.
I know all this because I do tend to put music into my novels and also dancing. In A Legacy of WarThere are the balls at the house party held by the bad guy, but even the WIP (aka The One About The War) has the sword dance.
So the next question is... can your characters dance?