Yeah, Ambro was NOT supposed to turn out like that.
Anyway, the process for making a Claymore in the manga is to replace a girl's organs them with a monster's organs.
So, half-monster would mean outward appearance is normal, but the organs of the Claymore would not.
Their DNA is still human, except for the monster organs. They think and act like a human, but that could change as a Claymore releases more monster energy (kinda like mutation caused by radiation, but without the harmful side-effects).
This picture shows a Claymore on the right and a monster on the left. (the Claymore has used her shape-shifting ability)
I would need more specific questions for more specific answers.