just write a simple batch file to start up your EQ sessions, and also have it delete the logs at the same time.
start /d "F:\Games\Everquest" eqgame.exe patchme
timeout 1
start /d "F:\Games\Everquest" eqgame.exe patchme
timeout 1
del F:\Games\Everquest\Logs\eqlog_*.txt
Pretty simple to put that into a batch file and away you go. I use the timeouts because if I just start all 6 instances at once, they won't login the last 2 or 3 of them quite often, but the timeouts fixed that.