What do you believe , is a confessional something that is sacred between
the the two parties involved ? or does it depend on the severity of the
crime/sin.
In USA, as long as the person enters a fiduciary relationship with the priest or authority, the law is very clear. The priest or other authority must report to the police when a person's or another person's life is at risk of harm. The rest, no, there's no legal obligation, and that's done based on the ridiculously false premise that priests and religious figures of authorities are supposed to have good morals and do the right thing.
The issue is if child sexual abuse is considered life threatening. That's part of the reason instead of calling those children "victims of sexual abuse" they call the "survivors of sexual abuse".