No, I'm not deciding that. I'm evaluating my experience of her, and my knowledge of her, and her past actions and past statements ("I'm more important than they are"), and my experience of their experiences with her ("all mommy had in the house to eat was cereal and soda pop").
And I'm wondering whether I can be available to help without violating my own boundary.
I don't have to surrender my fatherhood just because they're sleeping under someone else's roof -- someone who hasn't exactly shown the soundest judgment in the last 2 years, by her own admission.
Would your reaction have been different if instead of pain medication it had been unsecured firearms? Well, they might accidentally blow each other's heads off, but oh well - you're assuming she hasn't given each of them comprehensive weapons-handling instruction.
So if you want to talk about assumptions, you might consider starting by abandoning the assumption that every woman has your maternal skill-set.
As recently as the month she moved out of the house STBX did not know how to change batteries in smoke detectors. And you might recall, she asked if I could check out some work in her bathroom she was hiring an electrician for, because the light suddenly stopped working. After changing the bulb, I assured her an electrician would be unnecessary.
Where I live children do die from being with parents who don't quite get it. Mine are not going to be somebody's Mulligan.