All petz (even hexies) have the personality of one of the original breedz. Hexed breedz may have their own customized voice. Offspring inherit the voice/personality of one parent. They do not have a mixed personality. The personality can be inherited completely independently of shape or color. A cat pet can look exactly like one parent but act and sound like the other.
I have noticed, however, a tendency for personality to match ear type, especially after several generations. Most selective breedz will have ears that match the voice/personality.
Petz 5 has a pretty common glitch causing mute petz. If the petz is descended from an original breed, and that is the voice it is supposed to have, you can use the unmute utility from Odd-Petz
to fix it.