How can I get them to understand?

[ConfusedWriter08]

How can I get my younger children (DD9 and DS8) to understand how much their constant arguing and petty squabbling is affecting my mental health?
When I say constant, I’m not exaggerating. It’s literally from the second they get out of bed until the moment they fall asleep. He’s looking in her bedroom, he’s talking/shouting/breathing at her, he’s touching her things, he’s sitting next to her on the sofa, he doesn’t want to watch what she does and vice versa. She’s called him an idiot or a dummy (a whole other bone of contention), she won’t pause the tv, she’s moved his whatever. Then they go to bed at night and Alexa is constantly going off/pinging on my phone. He’s got Alexa too loud (he listens to white noise or piano music at night to help him fall asleep, ADHD), he’s trying to shout to her, he’s out of bed.
It’s so incredibly draining, and I feel like I’m a referee in the world’s shittest contest. We know that DS can be irritating without meaning to be as he gets bored easily, but equally DD is hyper sensitive and just picks at everything he does, usually defaulting to screaming at him. It seems that nothing I do or say makes a difference for longer than half an hour.
This morning I completely lost my shit and told them it makes me feel like I don’t want to live with them any more, and they just looked at me. I genuinely feel like I could leave for work today and not come back and all I’d feel is relief (for a good long while anyway). I dread being at home with them, and I loathe that I hear myself saying “sort your kids out” to DH whenever he’s here because I can’t bear to deal with them any longer.

Please, somebody tell me you’ve been through this and it gets easier soon?

School have no problem with either of them individually, and they don’t really mix at school as they’re two years apart. DS has a SENCO plan for keeping him engaged and stimulated and is thriving, DD’s teacher regularly tells us she wishes she had a class full of DDs.

A big problem is that DD regularly tells DS off for things or tries to ‘discipline him’ (for example if I’ve told him to go and brush his teeth and he’s dithering about she’ll start getting on to him to brush his teeth and he doesn’t react well to her telling him what to do. We’ve tried telling her countless times to just leave him to it and if it’s a problem he’ll get told off, because all she’s achieving is getting told off herself when they start arguing and fighting, but she just gets caught up in what she thinks is the right thing to do and forgets.

You’re ignoring everything that’s been suggested about seeking help for yourself rather than pinning all of the responsibility for your misery onto your children. Parenting courses, seeing your GP, finding new strategies to manage irritation and stress.

When you tell your husband to sort his kids you’re separating yourself from the 3 of them and they must all feel you resent and loathe them. It’s hugely damaging. And unnecessary.

What you FEEL is overwhelmed, ashamed, anxious, angry, resentful, panicked, powerless...

You absolutely do not FEEL like you can't live like this. That's a thought, an opinion, a mental process.

Your children will not understand how you FEEL because you haven't told them. They have experience of those feelings - indeed, sounds like they both have those feelings much of the time about each other.

Start witty talking about FEELINGS which they can understand, rather than your thoughts, which just scare the shit out of them thus increasing their own feelings of powerless, panic, anger, shame etc.

Perhaps your DD needs to be a little tolerant and on the other side of it your DS needs to learn to stay out of his sisters room, she's entitled to her privacy especially as she's older.
I'd be very firm about the screaming and hitting.