Just a quick update, I worked with Stablebit support and was able to remove all three of my 3TB drives from the pool. Two stalled at around 90% of the removal process, once they hit that I had to do a settings reset in Drivepool, they then showed as removed from the pool. The issue is 2 of the drives still had data on them in pool folders, thankfully I was able to copy the data back into the pool from those drives.