What I always do for characters that have VAs is to try and look out for HOW they express themselves. What types of words do they use, what language do they use in what situation, and where do the inflections lie in their dialogues. I also look for verbal tics or quirky pronunciations, and if possible I try to find video of the VAs doing the voices themselves to see if they do any hand movements or the like while saying their lines.

I don't know if that helps, but it's helped me in the past.