Kelvics cannot be Mixed Blood because Kelvics aren't a race really, they are a genetic mutation. So, either the player is fully human that carries the kelvic gene or they are a full blown Kelvic. There are no halfs. And also, the kelvic factor doesn't crop up in mixed bloods or other races, so you'll never have say a kelvic Symenestra for example.
Also, there are no half forms. The writeup is clear with that. Though, Kelvics do have some animalistic features (unusual eye color, elongated or sharp teeth, natural grace). We've got multiple help desk tickets requesting furry ears, tails, dog legs, etc... each one we've flat out said no.