Aww OP I empathise, it is such a daunting prospect when you’re shattered but you will get into the swing of it. My advice is lower your standards and get a decent carrier/sling!
What I do is prepare as much as possible ahead of the trips - so when DH is around to share the load, try to get to the bottom of the laundry basket, make sure you have essentials in (for me I now specifically check for coffee, milk, toilet rolls, dishwasher tabs and bin bags - sadly learned from experience!), get DH to batch cook a couple of meals for the freezer. I also get a load of Cook meals in so I have a nice meal I can microwave if it all goes to pot! Also look ahead in your calendar before he leaves and share out any associated admin to minimise the stress of last-minute curveballs - eg a birthday you’d need a present for, a dress up day at nursery you’d need a costume for etc.
I always feel much better if I go out, even though it can take ages to actually get there! I often just walk to the local supermarket with a cafe - it combats the loneliness, gets everyone fresh air and it’s one less meal to cook!
What specifically do you think might be challenging about the mornings and evenings in particular? Is it getting things done for a set time, that so much needs doing at once, or something else? Just wondering if there’s anything practicality-wise we can help you think through. Eg our toothbrushes live downstairs and I have a changing table with all baby’s nappies, clothes, dummies etc by the back door so I don’t have to keep running up and down stairs and can do a speedy last-minute nappy change as we’re leaving the house if needs be. If you can think about what specifically you’re worried about we might be able to help with solutions!
If it’s more about timing, one thing I found helpful in the early days was working out a mental priority list…so eg baby’s first milk trumped eldest’s breakfast, but as soon as milk was done I moved onto breakfast, even if it meant putting baby in the pram to cry for a minute. And a tip I read somewhere helped a lot - I vocalised to baby that they needed to wait, and why, so: “I’m just putting you down for a minute to make your brother’a breakfast, you just need to wait for a minute then I’ll come back.” Obviously baby doesn’t understand yet, but it’s really good for eldest to see that they’re not the only one having to wait constantly.