My SS does not have ADHD, but can be as slow as molasses. We joke that he runs on his own time. We once were on vacation going out to a nice dinner with reservations. We told the kids, "Anybody not in the car in 2 minutes is being left behind" and he ran out to the car with his shoes and socks in his hands as we started the car. He lives skin of his teeth sometimes.
If there's anything we really need him to get to, we tell him to be there earlier than he would need to be. Or if we needed him to get up by a certain time, we'd wake him before anybody else.
Your mileage may vary, but maybe if you know your oldest tends to need more time, whatever the reason for it, he gets woken up first. Then you can focus on the 7 yr old.
How much do you have them do at night? Was the outfit his pick from the night before or your pick from this AM?
And, while it would be better if the kid brushes his teeth every morning or had matching socks or all his schoolwork, if sometimes they go without and learn the hard way, maybe they'll change. When my stepson was younger and would have a crisis because of his own dawdling, we'd try to stay calm and remind him that he doesn't have a choice not to go to school (or whatever) but he does have a choice how he gets there - with matching socks, with a good lunch vs two things grabbed at the last minute, etc. When he was in HS, he would miss the bus and we charged him "cab fare" for us to take him in. When he complained about the steep price, we simply told him that he had a choice. If he didn't like it, he could get ready on time.
It is sometimes very hard to be calm when you know you have to be on time and the kid just isn't moving. Hang in there.