Hi,
Copyright laws are a bit of a briar patch, so you would need to consult with legal counsel about your specific rights. Also, you can visit Apple's legal website at the following link:
Legal - Contact Us - Apple
For information purposes, everything on iTunes is copyrighted. When one "purchases" an iTunes song, one is purchasing not the song itself or the copyrights but rather a license to use the song for personal, noncommercial purposes. There might be a copyright issue if one uses the song in an iMovie project and then publishes the project on social media or the internet. Arguably that could take it beyond personal use. If one receives monetary benefit from use of an iTunes song, that could constitute prohibited commercial use.
So, the safe route would be to get the written permission of the copyright owner.
-- Rich