2. calligraphy should say something like "Given by John Thompson to Scarlett Li and Christopher Morrongiello to commemorate the happy occasion of their wedding. Painted by Bai Yunli on......(date). Scarlett's Chinese name is 李虹. For his name she has selected: 克瑞斯•慕容吉樂. Of course I am 唐世璋.

According to my understanding 慕容 is an old family name and today there are Chinese people with the name 吉樂, so I think 慕容吉樂 would be fine without 克瑞斯. Perhaps when the actual scroll is made you could put the full names in Chinese and English on the scroll label (back of scroll), like this:

古琴與魯特琴合奏﹕for 克瑞斯•慕容吉樂 and 李虹 from 唐世璋 Qin and lute play together: for Christopher and Scarlett from John