Do the voice for one character at a time then work on the next one.

Try to make the voice memorable enough so you can remember how to do it the next time if you can't do it all in one sitting (sort of like how impersonators can get into the character of the person they are impersonating).  Develop the voice so you can go back to it without having to work on it and then do the voice work.

Give yourself plenty of breaks.

See if any of your friends are willing to do voice acting to help out.

WARK!

Thus Spoketh Winterclaw: a blog about a Winterclaw who speaks from time to time.

 

(using Poser Pro 2014 SR3, on 64 bit Win 7, poser units are inches.)