I believe guys like you en me (I'm a slow player, so fast fights/strong enemies are really a problem for me!)
have most profit making yourself a Priest. Let do the Summoned compagnons do the job
You can take first Summon Ghost and/or Summon Undead (later on take Summon Demon (you can unlearn all your skills later in the game and relaern new "higher level" skills).
Have you already find a way to summon your Creature to help in battles?
Skills like Stun Arrows, Hide in Shadows, Healing, Charm etc can give you more time.
With Amdusias it's important you force him to go in melee so his is stopping using Explosive Arows (very deadly!!). Your Creature with a Ghoulish Head (Rush Attack & Fatality skill!) can help you with that.