D.D.
Mom of 4 here. Most people think that allowing more time in the morning would make everything run better. I found it to be the opposite.More time it gives more opportunity for them to argue and pick at each other. I always planned just enough time for them to dress, groom, eat breakfast and get out the door. The spillers ate breakfast first before dressing. The careful ones would dress and groom first before eating breakfast. They each had their own routine which was suited to their needs and kept the mornings moving without bickering. Was it always perfect? Nope but it worked.
At 9 and 11 they can understand directions clearly. Let them know up front what's going to happen and tell them that if they are going to argue then they aren't going to be speaking to each other for the morning. Then try to keep them out of each other's way.