The first one you will come across will be Ruen T'Dax and he has a buddy with him. Ruen T'Dax is level 36 ^ ^. His location is -7.66, -24.04, 63.29 in the second level of The Tombs of Night. After you finish killing Ruen T'Dax you will get the dark crystal need.
Now you need to head to the path that leads down to the lowest part of The Tombs of Night. Vieya N'Larn is located at the following location -100.30, -24.13, -17.00 . She is a lvl 36 ^ ^ with two friends. After you destroy her you will receive your vial of noble blood.
Once in The Crypt of T'Haen you will need to find the dark altar. The location of the altar is -108.79, 26.76, -7.54 . It's a lightpost with purple light coming from it. Surrounded by Bloodsworm backbiter's and soldiers. Right click the Lightpost and go back to Laren Jadefire and turn in.
Laren Jadefire has ordered me into the Tombs of Night to find two specific vampires and slay them for a darker purpose. Once I have done this, I am to enter the Crypt of T'Haen and find a dark altar. I am to use what I gained from the two slain vampires on this altar to perform a dark rite.
I have been ordered to kill two prominent vampires within the Tombs of Night. They each possess something that is to be used in a rite I must perform.
Laren has written instructions in my journal to kill a vampire named Ruen T'Dax and acquire a dark crystal from his corpse.
I have slain Ruen T'Dax and acquire the dark crystal he carried.
Laren has left written instructions to kill Vieya N'Larn and take a vial of blood that she carried as a memento.
I have slain Vieya N'Larn and acquired the vial of noble blood.
I have slain both vampires and gathered the required elements of the rite as ordered.
I must complete a rite upon a dark altar within the Crypts of T'Haen and then return to Laren Jadefire.
I must find the dark altar within the Crypt of T'Haen and use the crystal and vial I gained to complete a dark rite upon it.
I have completed the dark rite upon the altar which imbued the crystal with a dark presence.
I must return to the Brethren of Night encampment and report to Laren Jadefire.
I have spoke with Laren Jadefire.
Laren has sent me to speak with K'Shar Haelbreng in the Brethren of Night encampment.
I have spoke to K'Shar Haelbreng.
I have completed the dark rite and eventually spoke with K'Shar Haelbreng.