Just finsished this on Core with two characters - an FMT and an Inquisitor. It really was quite easy. FMT used mainly longbow and longsword&shield, and the INQ went shield + axe,/morning star/hammer (for Conlan's hammer). INQ finished as level 21, can't remember the levels for the FMT but they were about 13/13/16 or something.
The main strategy was to boost the ac and thac0 for the inquisitor who then goes hand-to-hand with any and all enemies on screen, while the FMT shoots arrows and spells/buffs from behind. This strategy was viable for basically the whole game through. Both Yxunomei and Belhifet fell quite easily, with only 3-4 reloads. I planned too lazily first and was punished. With proper micro none of them proved a problem. If any enemy melee-attacked my FMT, I just quickly set up a mirror image and some more buffs and hack them down in melee, temporarily using the Inquisitor to assist if necessary.
The repeater longbow solves a lot problems for example in the Severed Hand, as that bow combined with haste allowed me to interrupt spellcasters quickly and effectively for the Inquisitor to then easily hack them down.
The Inqsuitor wasn't as overpowered here as in the BG series, mainly due to true sight not being as useful (the invisible theves in Dorn's Deep being an exception) and dispel magic neither being that frequently used. Dispel Magic was effective in the early part of the game for getting the FMT out of trouble if suffering from some negative effects. Of course protection from evil was useful for the AC boost, so there is that.
The whole point of the excercise was to get my duo to the Heart of Winter and Trials of the Luremaster expansions, and see how they fare in the expansion. The suspicion is that it won't get that much harder. We'll see.
I remember the first time I faced Belhifet with a six member severly unoptimized party. That was not fun, and it came close to being a fight I thought I wouldn't be able to win. So it was pretty fun to see how easy both Yxunomei and Belhifet went down in this playthrough.
Overall, replaying Icewind Dale felt less grindy and more engaging than my recent 4-member party BG and BG2 playthroughs.