I chose mine based off the personalities of the characters I was creating. Gogon is a seeker of knowledge and holds information in high regard, as such Thaliak was the obvious choice for him. Chachan follows more closely to his family's heritage and is a smith, and thus has Byregot. Judge has a very black and white view on things and believes one thing will lead to another, and so I picked Nymeia for him. That's just personal preference, though. 
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