By being ruthless about what we do, and when we do it.
DH and I have both been working from home full-time in demanding roles (senior finance and IT) from the middle of March with a now almost 4 year old DS, and almost 3 year old DD (who also has SEN).
We worked out early on that we needed a rota for splitting the day in half, then each dedicating half the day to looking after the children, and the other half to working. We then do additional work hours either early (usually me), or late (usually DH).
I also try and do half an hour exercise daily at 6am, though in reality it usually happens 3 times a week. We have cleaners who come in once a week, and keep the place reasonably clean in between. We're also getting a gardener once we've finished landscaping the garden.
DH batch cooks 2 or 3 different things on the weekends, so that during the week we only have to add rice, pasts or whatever else to our already made stew. We don't eat ready meals, everything is made from fresh.
We also only do washing on weekends, it goes in each persons washing basket, and stays there until I've sorted it all out. We don't have a dishwasher or dryer, so plates etc washed by hand, and clothes hung up on airer. We don't iron anything (!).
I do our weekly supermarket shop early on a Saturday morning, so I'm home by 9am, and don't have to interact with a lot of people as not many about.
I have a lie in until about 10am or sometimes later on a Sunday, as it's the only day of the week that I'm not up by 6am.
I don't feel stressed at all OP, so hopefully some of what I do in my routine may help you.