For the first and second questions, that's completely up to player preference. The creatures behave in the way their people perceive them - they can behave like the animal whose shape they take or just be the perfect pet/companion, they can need to eat or not, etc. They can eat each other if they have a need to eat, but only if both players agree to it! They can be killed, but they are sturdier than a regular animal.

Let us know if you need anything else!