I'm sorry OP, that's tough and stressful and hard. But where the hell is the discipline here? You sound so overwhelmed that you can't see the wood for the trees.
Let's just break it down and realise that these are all things you can absolutely cope with.
X not walking when we got to town, having to carry them both into the bank
Why? Is X able to walk? Why are you carrying both? Why no pram? Why not tell them to walk? What are the repercussions if they choose not to walk? Do they just get their way (carried)?
them screaming all the way home from the bank
Why? How did you handle this? Were they disciplined/asked to stop? Were they hurt or upset or just like making noise? Did you try a distraction?
then shouting ‘where’s the remote’ repeatedly
As above - why? What did you do about it? Did you step in or explain it's unacceptable?
Y screaming banging cupboards and my legs whilst I made it
And you told him off? Removed him from the cupboards? Distracted him with a toy or with "helping" you prepare food (literally "could you please be my helpful assistant chef and hold this packet for me until I need it?").
refused to come to the table so I brought him there
Good, good for you.
he slapped me three times and scratched me
Oh boy, you do not deserve that. You should not be hit or scratched by your own child (or anyone else). No. What did you do about that? Take it?
they ate my breakfast I made.. well licked it
And you did what? How did they even manage that? What was the consequence for that?
I want food but I have to sort them out first
You have sorted them out. Their food is on the table. A 2.5yo can feed himself. Put his food on the table, feed yourself and help Y if Y can't feed himself sufficiently.
Y is covered in beans along with the table so everything need to be cleaned
Good - they're supposed to be covered in beans. That's fine. A quick wipe is fine. Children are allowed to be covered in beans. Lower your standards here - you're fine.
X refusing to eat anything even though he’s hungry
The food can wait. No reaction. You eat, Y eats - X will make his way when he realises Y is getting attention for eating but he's not getting any for refusing.
they’ve now ripped the curtains down from in the kitchen and are running around the table chasing each other with it
And where's the discipline? Take it off them. Sit them down, tell them no, explain why it's wrong. Teach them how to behave.
there’s food all over the floor and table it’s going to need a wash
Mess is fine. It'll take 10 minutes, if that, to fix - it's fine. Mess is fine.
None of this is something you can't fix or cope with or sort out. You're just overwhelmed and stressed. Breathe and chill. Cool, calm, collected - discipline them when they act like this, don't give in because it's easier in the moment because it'll be harder later on. You're doing fine.