Help House of Grief fight is just insane

Darkness spells. Them Mf’s Sharrans are slinging Darkness all over my party and there seems to be nothing I can do about it.

I tried casting dark-vision and Daylight but nothing seems to work. My party are blinded and cannot use any ranged attack whatsoever.

How the hell do you counter darkness spell?!

So far my party has survived the longest by retreating to the stair and conjure Evard’s black tentacles but that pretty much means I have to sacrifice Shadowheart while the rest of my party stay behind the Tentacles.

Even then the Sharrans will still blind the rest of my party with Darkness leaving me unable to target their spellcasters. Even worse is some of them will then use Shadow Step to teleport behind my party, negating the Tentacles. Doubly worse is their Darkness spell would dispel Guardian Spirit and Cloud Kill, my best AOE spell. What gives?!

It’s also rather unfair that they can still target my party-members while we are shrouded in Darkness. Also stupid that even if I set Gale to stand atop of the stair, away from the Darkness spell at the bottom, Gale still can’t use any spell because they seems to also interrupt line of sight.

This Darkness spell is the Be-All-End-All spell, I swear.

How the hell do I beat this fight.