You're in the thick of it now, 1>2 + 3>4 is so so hard, and to top it off you must be feeling so tired as well being pregnant with twins. You can't see yet how wonderful it's going to be!
There will come a time when your eldest is 5>6 and your second is 3>4 and suddenly you will be able to send them downstairs to watch TV for a bit so you can have a lie in, or out to play in the garden whilst you get something done. And they'll chatter away to each other, play imaginative games together, cuddle each other, look after each other. Not only is it easier but it's just so much more rewarding as well. What's great for you is as you reach this point your youngest boys will already be 1+ so you won't have much longer to go until they catch up and can join in with the older boys. You'll have 3 years where they're all at primary school together, which will be awesome.
There is something so magical about 4 boys and in your case especially so, because they are all so close in age they will be a proper little gang. I find that little boys can be gentle, creative, polite, sweet and kind just the same as girls. And that little boys love colourful, beautiful, sparkly and cute things as much as little girls if they are given the chance to express that.
As grown men they have the potential for wonderful enduring friendships with one another. That can actually be harder for men, so what a gift to have from childhood! And you will have 4 men to help, support and amuse you.
I've got 3 and when I was pregnant with the last, I thought twins would have been terrible. But now I look back and realise that was my only chance to have 4 really, as I have no desire to return to the baby phase with a big gap now. Now that I have 3, 4 seems manageable in a way that I couldn't conceive of when I was stressed out with just 2 (like you, at ages around 2 & 4). But it's the ages that make it so hard, and they do grow easier and much more fun, and quickly too, in the scheme of things.
Have you told your little boys about the pregnancy yet? I would lean into their excitement about getting two cute little baby brothers at once. It is so exciting!
There's a lovely book called "The cat who wanted to go home" about a little french cat who accidentally crosses the channel in a hot air balloon, and desperately wants to get back to the 4 little french boys she lives with. Its got this lovely imagery of the 4 little boys lined up next to each other like a set of steps.