You shouldn't fear cooking two or more briskets. My suggestion would be to get comfortable with the outcome of a single brisket before trying two.
One suggestion when smoking multiples, choose briskets that are similar in weight and conformation...especially the flat end. Look for the thickest ends you can find. They may not finish at the same time but they should be close.
You didn't mention which smoker you're using. General rule of thumb, cook fat side down. This will help protect the meat side from the closer proximity to the heat elements. If cooking two, rotate them (top to bottom) at the 160 plateau stage. Again this assures a more even heat distribution.
Hang in there...you'll get good results in time. Keep notes on your cooks and have a look at SmokinOkie's Brisket 101 found
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