Hi Debbie,
I dont think he has any intention of stopping, if he’s doing it with his son, then he sees no harm in it, and until he sees the harm he wont face it.
You have done all you can to suggest you talk before his kids arrive, but he doesnt want to do that, they never want to talk, because he wants to carry on doing coke, and you dont want him to, there is no compromise to be had.
Its just about damage limitation, you need to protect yourself, if he’s not willing to deal with the elephant in the room, you shouldnt be expected to live with it either xx