1. Are there ethical principles fiction must adhere to? What are they?
No.
There are principles MY fiction must adhere to.
There are principles the story I want to read and like must adhere to.
Depending on where and when you live, laws and ethics are different, and that colours what people see as ethical.
Depending on who you are, what you see as ethical may be very different from what I see, or the next person.
A universal ethical principle doesn't exist.