Wow. It sounds to me like you're doing an amazing job already. Don't underestimate how well you're doing already.
But also no wonder you're tired. As booyhoo said, 8-12 weeks is a bit of a bonkers feeding frenzy ime. And it really drives you round the twist as it can seem totally relentless. Your own needs are totally ignored. It's terrible!
School holidays are really hard at the best of times as well.
So, stuff you can do to make things easier in the mornings? Sorry if this sounds at all patronising or you already do it but I find it helps me a lot.
I lay the breakfast table at night with jam pot, sliced bread out for the kids. All dh has to do it get out the juice, milk and yogs. It saves me 20 mins in the morning when there are far more people milling around.
I have shower last thing at night and in the mornings, just have a general wash. Saves time.
Cooking. When cooking, make twice as much so you can freeze half and serve it up the following week.
Play dates. Have your older kids got any pals you can send them off to for a couple of hours?
Early nights. AT least one night a week go to bed the same time as all the children. Pack them off early if you have to. Even if you're only lying in bed reading, you're resting.
But good luck. You're doing very well and it's little wonder you're tired.