The first 2 are my favourite carols, but they do sound better when sung and played in tune, and accompanied by a church organ rather than passing traffic.

Would you believe that YouTube notified me of copyright infringement,
as these carols are allegedly owned by Warner Music?

They're talking rubbish. The carols have been in the public domain (out of copyright and not owned by anyone) for well over a century. Streaming a recording of them might arguably be infringing the copyright of the performers, but they aren't Warner Music.

I'd tell YouTube to ask Warner Music to notify you themselves about this "copyright infringement" and dare them to threaten you with legal action. Then they might realise the absurdity of it.

It was just an excuse to stick adverts on it, and you can't argue with YouTube.