Certainly the ones who’d attained “priesthood” as priests and counselors etc. are mandated to report it. But quite often in family incest cases if the other parent knew and did nothing they are regularly brought up on charges.
Yes, of course. And that is because the parents have a legal DUTY to protect their children. I'm not familiar with the legal duty of priests to report crimes. Last I heard there were things such as "spousal privilege", "priest-penitent privilege" and "doctor-patient privilege".
Perhaps there are some people within the FLDS that have a DUTY to others, but it isn't necessarily the case that ALL of the adults have a duty to protect ALL of the children.
Do you have a legal duty to protect your neighbor's children? Do you have a legal duty to protect the children of people who attend the same church you attend?
If you believe that your neighbor is smoking pot, do you have a legal duty to report them? If you fail to do so, does that make you an accomplice to their crime?