You should be able to open up 5 copies of WoW without issue, or at least without error messages. Try to open them up without logging in on any of them, because logging into the same account on more than one instance of WoW will kick the first instance offline. See if all 5 actual open just by running wow.exe 5 times.
If so, cool, you'll be able to do it. Try it with trial accounts then, setup 4 trials, login on the first WoW with your actual account, then the 4 trials on the 4 other WoW's. Go from there!
If you're getting an actual error message, let us know what it says and if it's actually generated in-game, or if it's a Windows error with the "Send" and "Don't Send" buttons and such.
Cheers
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