That’s not how commission works, Alton Towers paid for the music and all copyright would belong to them. However for some reason the CD contents are different, so IMAscore must have struck a deal with them.
Not necessarily, I've been in the entertainment business, when ever I had commission publicity photos or a promotional video, unless otherwise specified in writing, the person that films or records me actually holds the copyright to those images/video, I can only imaging the same would apply for the CD contents.