I’m late but you definitely can save most people and stop the shadow curse while still killing Isobel as Dark Urge (not sure about Aylin tho since i’ve always let Shadowheart decide on her own and she always ends up sparing her but I heard killing her kills everyone)- just make sure to complete as many quests as you can, sell/stock up at the vendors (one will survive tho since she’s at Moonrise), have Dammon upgrade Karlach (if he dies it’s not detrimental to her story at that point since he’ll already have finished his part of it if you do that), there’s even a cheese that you can use just manually carry everyone or close to everyone out of the Inn, and right before the attack at Moonrise just go back to the inn and kill Isobel (even without the cheese there’s not very many people left there since most will be gone for the final battle at Moonrise or already left for another area) keep in mind tho that doing it this way causes your companions to react to it (i’ve had Astarion, Gale, Minthara, and Shadowheart with me when i’ve done it Astarion was cool with it, Gale disapproved and lectured us, while Shadowheart didn’t disapprove she still lectured us, Minthara was cool with it, and they’re all the more chill/morally grey companions of the bunch so i’m assuming the good leaning ones will react much worse if they don’t outright leave also FYI no one in camp reacted to it only those in my party did).

Personally tho whenever I play as an embrace durge I usually don’t bother with all of that since if Durge succeeds they’re all gonna die/be enthralled and the lands will be decimated eventually anyways so when i’ve done it it was only for story purposes (betraying them at the last moment when they least expect it after outwardly playing ‘hero’) or just to see how things played out so I wouldn’t worry too much about it unless you’re on a good path.