put a brisket on the top and bottom rack. Then you can put a pork but on each rack also, but 2 7lbers should fit on 1 side of one of the racks if you want to do it that way.
Biggest thing is that your briskets will probably finish before your pork butts depending on what temperature you are cooking at. As long as you check on your meat from time to time, you shouldn't have to worry about burning anything.
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