Or it could be 'Watch' as in 'Guards'.
So the Master of the Watch is the guy in charge of supervising the security and defence of the fortress-monastery. Which is a position I can see 2nd company captain having if 1st is 2-ic (ie admin until CO is out of action for whatever reason) and third is armourer.
The rest are indeed, fairly self-explanatory. Although 'Marches' may mean perimeter security, or it may mean supervising the admin of what units are on deployment, or maybe even recon - as the Scout Captain appears to be in charge of the recruitment process, not actual scout deployment.