As was mentioned, that middle archer is going to die really quickly unless defense boost or attack down gets put up ASAP. Aside from that, in most cases all you need to do is toss out Regen to any archer that needs it and it should be sufficient to keep them alive in most cases, although if you see any that are fairly low on health (around half) you can throw them some cures as well.

Something I've been doing lately, although I don't recommend it until your group is used to Hamlet Defense, is to gear up for Magic Attack, use Cleric stance, and pull a few enemies with a Stonera and/or Aerora to the rear lines which are usually standing around not doing anything when enemy waves first arrive. Not only does it take the heat off the first middle archer, it makes the enemies die a lot quicker as with them spread out more archers are attacking them. I'd take off Cleric Stance once the boss arrives though as sometimes you will need to spam heal whatever facility he orders them to attack.

I'd say gear up for Magic Attack in general in Hamlet Fights when you are a bit more used to it. You can help finish off weakened enemies which is many times more beneficial to NPC survival than simply healing. Just be very careful not to defeat any of the special-weapon enemies.