I'm not sure giving her ultimatums is going to help the OP. If this marriage ends she will get the house, the kids, and an income off the OP for life.
It will be for him to prove that she's a dopeheaded unfit mother, not for her to prove that she's not. He married her, ergo he has to keep and house her forever, end of.
Before doing anything else, I'd want proper advice on what the actual legal exposures are here. You can't just accuse her of being a dopehead and expect to be believed. You'll have to prove it. If you can't, you'll look bad, not her. Even if you can, you may still look bad:
Judge: So what'd this unreasonable behaviour by your wife you complain of?
sunshineandbooks: She's a pothead, m'lud.
Judge: Since when?
sunshineandbooks: Long as I've known her m'lud.
Judge: Oh, right, and it's only just started bothering you now? Don't make me laugh. You're another, you hippy. Give her the house, you liar.
I have no idea if that's a possibility, but it might be worth checking it out. Also, what happens if she accuses you back? Maybe you're a racist, or a whoremonger, making up lies to make her look bad.
It might be wise to find a way of getting her drug addictions documented somehow. This will take careful thought because if you produce a video of drug stuff in the house she can just say it's yours. Is there any way you can get her on film doing it, maybe get her arrested in possession a few times?
Failing that, there's always "Strangers on a Train"...