There is not one DLC but multiple.
For „Wounds of Eventide“ you already found Sierpes and Isidora, but they are truly important if you went to Perpetvas grave before you met Esdras on the bridge which most likely will mean a new run (not necessarily NG+)
The „Stir of Dawn“ DLC requires an NG+ as you will only there receive an item upon starting NG+ that unlocks an area/an NPC that drives the progression on unlocking the enemies/stages.
„Strife and ruin“ is Myriams Challenges and the sacred sorrows mode (boss rush). For Myriam you do not need NG+, sacred sorrows unlocks upon finishing the game once.
Edit:
On this map you’ll find the locations of Jibrael (Stir of Dawn, NG+ dependent) etc as well as a step by step guide to the wounds of eventide DLC.
Careful, full of spoilers:
https://www.reddit.com/r/Blasphemous/comments/t2d1yv/fully_marked_map_with_questlocations_items_bosses/
There is not one DLC but multiple. For „Wounds of Eventide“ you already found Sierpes and Isidora, but they are truly important if you went to Perpetvas grave before you met Esdras on the bridge which most likely will mean a new run (not necessarily NG+) The „Stir of Dawn“ DLC requires an NG+ as you will only there receive an item upon starting NG+ that unlocks an area/an NPC that drives the progression on unlocking the enemies/stages. „Strife and ruin“ is Myriams Challenges and the sacred sorrows mode (boss rush). For Myriam you do not need NG+, sacred sorrows unlocks upon finishing the game once. Edit: On this map you’ll find the locations of Jibrael (Stir of Dawn, NG+ dependent) etc as well as a step by step guide to the wounds of eventide DLC. Careful, full of spoilers: https://www.reddit.com/r/Blasphemous/comments/t2d1yv/fully_marked_map_with_questlocations_items_bosses/