The Amazon UK site has samples of the Peace Deluxe songs. It lists the soloists!
Lullabye - Jakob, Ben, Josh - Wow! So is Josh on the high notes and Jakob on the low notes or the opposite? It would make sense that cousins's voices would sound similar and blend so nicely.
Eternal Light - no soloist listed? Says the composer is Akira Senju.
Have Yourself a Merry Little Christmas - Ralph, Mini James
Silent Night - Ed, Tom - It gives them in that order.
You can see it here: http://www.amazon.co.uk/Peace-Luxury-Edition-digital-booklet/dp/B0047BVEWQ/ref=sr_1_1?ie=UTF8&qid=1287228792&sr=8-1.