BeI get the strong impression you are a powergamer more then a Role Player
If that is the case it's indeed very usefull to have a Kensai wielding Celetial Fury and Crom Fear to do Massive damage and the Barbarian as Shield (but it might be better to use a Beserker instead) the Inquisitor can come in handy though dispell magic can be gained from Carsomyr aswell
I just do not see the use of 4 Fighter-type characters in your party
if you would take on the priest i admid he won't be a good fighter but he's a better healer then a thief/cleric and you'll need it
Also an assassin is not someone you send in for melee combat but someone you use to backstab a mage and give poison damage so the mage won't cast spells during the whole battle After that attack you can withdraw you assassin equip him with a bow and attack from range, this way your inquisitor won't have to attack from range and can fully use Carsomyr
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The Rocks show the way