Heaven forbid one of your children finds his stash in the house and takes some, becomes seriously ill and dies, or is left brain damaged and in need of care for the rest of their lives.
Presumably he is in a job where he has responsibility over others, given what you said about safe guarding. A healthcare professional or a teacher maybe? You're knowingly putting the people under his care in danger by not reporting that he's a drug addict and under the influence!
On top of all of this, you're the one whose name and and bank account details are being used to buy all this stuff, you will almost certainly be held accountable as a drug dealer as you're admitting you know he's doing it and aren't stopping him.
Tell someone NOW, or forever have to live with the guilt if he, one of your children, or someone he's responsible for, end up seriously hurt or dead.
I genuinely have to ask, how, as a parent, can you let this man be living with your children? Be left in charge of caring for them? Be willing to put HIM before THEM by not getting them out of this situation? Because if this all comes out later, you'll probably lose them.