Evidence of sexual abuse by dad

My SIL recently discovered her husband has been sexually abusing their two young boys and has reason to believe he’s taken lots of pictures of them. Unfortunately due to their ages and the state we live in, the legal system has thus far proven ineffective in terms of protecting these kids. We’ve been told that under the age of 12, we need some sort of hard physical evidence or there’s nothing much they can do. (!) We want to go after the evidence as we would setting a goal for more moneys etc. I just keep thinking, “The evidence is out there and we will find it and we don’t have to know how.” Then keep taking massive action toward looking for it (hiring a PI, using a 3rd party to search the dark web, subpoena any records through the divorce we can get our hands on, etc.). Are we going about it the right way or would you recommend using thought work in an entirely different way? Thank you!