Who says Disney magic isn't real?
According to Hollens' YouTube page, he only makes music using just his voice and mouth (think, Pentatonix), which makes this video all the more stellar. Peter and Evynne sit in the boat, singing the song, just like in the movie.
A.) They're both real people.
B.) Different cuts of Peter singing the background music for the song are intercut over the main image.
Watch the video and listen for yourself.