Brother-in-Law 25M behavior is disgustingly concerning and predatory. Years of lies, deceit, manipulation, and abuse

I have known my brother in law 25M for five years now. Since the time I have known him there has been constant drama and situations with him and other members in our family. I need help figuring out what to do because his behavior is predatory and dangerous. What can we do to prevent this from happening again?

Some offenses from lease serious to most: -can never keep a job -lied about having children at jobs to miss -lied about having a sick mother -lies about stealing -stole and sold off his cousins shoes -dated his underage step cousin -repeatedly cheat on his baby mother -sx asult on his younger sister -has tried to flirt and sxt with family members -tried to sx a*sult my younger sister 16F

I am deeply concerned and have no idea what to do. His family is at their breaking point because this morning he texted THREE family members trying to send them a photo of his p*nis. I do not understand how someone can think that is okay and keep trying to rationalize why its ok to send a photo like that. am not sure why they protected him up until this point or what to do.