I'm so sorry to hear this. I'm angry on your behalf too. It isn't right.
I don't have any good experience in this sort of thing, but trust WF and kml and the others here who had dealt with MLC and substance abuse crazy. I 100% agree that in as much as your long-term goal is ensuring your kids' safety and happiness, it makes sense to gather information and talk to your L before talking to your ex. I'd recommend thinking through every step and deciding if it is more likely to help or hurt your long-term goal. In/re the idea of emailing him-- knowing the irrational and unhealthy place he is right now, can you imagine any good coming of that conversation? Is there any chance in h3ll that he'll be able to listen? I'm afraid that the likely outcome is what WF says, and the kids will be told to shut it, and your ability to hear what is happening may be curtailed.
If I were in your shoes I'd be scared about the what ifs (I fall prey to this a lot though). I guess instead of going off against your H before you're fully prepared and have everything that you need to be documented documented, I'd think of how you might give the kids the tools they need to be safe in the possible situations. Just like you've given them phones-- have you talked explicitly about when to call you? What it is okay to say no to daddy about, like not getting into a car with him if he's been drinking? Does S12 know how to handle a fire extinguisher and call whatever your equivalent is of 911? Do they have find my iPhone or whatever equivalent on their phones so you know where they are? Make sure they have some granola bars or something in their bags and water bottles when they go over there so they'll always have something even if your ex totally spaces on feeding them? I know you shouldn't have to do this, and you don't want to scare them. But they're great boys, they'll get through this, and I was babysitting by the time I was 12. It is not too early to learn about some of this stuff (and maybe they have already). Maybe a consult with a child psychologist isn't a bad thing either, both to get documented third party evidence and to get some guidance on how best to support them as they deal with their dad now and into the future.
All of this with the big caveat that I am not an L or a child psychologist and this could be all wrong... and I don't know the laws in your country (like here is might not actually be a great idea to go to a psychologist before you had all your ducks in a row, since they're a mandatory reporter and you might find yourself moving more quickly than you'd like in that situation). All just ideas for you to take/leave/discuss with your L. But just wanted to know that I'm thinking of you, I'm hurting for you and those sweet boys, and that I believe in you.
xx M
Me (46) H (42) M:14 T:18, D9 & D11 4/19 - 12/19: series of escalating BDs 9/20 - present: R and piecing