IMO I wouldn't drag my kids into this.
Please have an IC help you with this discussion. Do not let your X drive this bus. Do not use your kids as a vehicle to wake him up. It didn't work when he was having his As, it sure as shit won't work now.
Your children are small. Mine are too.
Until you know where your head is at I wouldn't bring them into this. They don't need to know. If major change happens like he is moving out you can have that discussion then. Again, get help from a professional for this. You are likely not in the right head space to be having this discussion.
You don't have a real chance of R. He is still blameshifting, rugsweeping and gaslighting the fuck out of you. Even if he did start doing the bare minimum for R I would not even attempt it until you are much further down the line.
Telling your kids there is a chance will confuse the hell out of them. Its sole purpose is to assuage his guilt. To keep you on the hook.
What they need is for you to be OK. Work out what will make you OK and start doing it. Like yesterday.