To: Ok I hope this doesn’t get too confusing but I seriously need advice please.
Me: You are damned if you do and you are damned if you don’t. Either you leave things be to sort themselves out and keep friendly with your sister, or you report him to the police and let them investigate him and her kids and decide if he is a P*** and lock him up, probably for a long time – but you will probably lose your sister in the process and you might alienate your family against you too.
If there is an “anonymous” police reporting telephone line, then that might be the only way to go, you can dob him in without getting involved yourself and if anyone asks if you know anything about it, say NO and keep your feelings about him to yourself