OK,
What would you have done differently? And understand, you’re dealing with a tight knit, very mobile, super-brainwashed group that has been doing this for a generation or so.....and sees nothing wrong with it.
OK, your turn....what would you do?
Arrest the suspects, try them fairly in a court of law, and punish them to the full extent of the law if found guilty by a jury. Protect the specific victims through a witness protection program. Leave the remainder to stay at the compound if they chose to do so. The arrest and conviction of the few scoundrels and perverts who are guilty of sexual crimes would break the cycle of abuse in any case without massive social engineering.
Here they needed to just develop some independent indication that underage girls were pregnant. Not just the third party relayed phone call. Notice I said indication, not even real proof or evidence.