I'm doing something similar.
Good news, butts and briskets both are happy at 250F. If you shoot for a top grate temp around 250F, you'll probably have both meats done in about 12 hours.
If you want them for lunch on Wednesday, fire the pit around 7-8pm on Tuesday. If you're having them for dinner, fire the pit just before you go to bed. Be ready to check meats on Wednesday morning when you get up, and expect to be busy poking that brisket throughout the morning. When the meats are done, foil them and chuck them in that cooler then get back to the fun stuff. They'll be hot and ready when it's time to eat.
Use the minion method with as much charcoal as you can fit piled up in your charcoal ring. Use Kingsford Competition if you can get it locally, it'll give you a good consistent burn and significantly less ash than KBB, which means your fire won't choke itself halfway through.
My cook is going to be a little more challenging, I'm doing a couple butts and a couple turkey breasts. I'll be putting the butts on in the evening, then putting the turkeys on first thing in the morning. Both need to be done around lunch time, and I know the turkeys take about 4 hours.