I found both of the targets you mention just fine. But you could be having the problem I'm having with those. Have you found all the other targets just fine?

Also unable to find Bulag in Shornhelm. was able to find all the others

OK, so I had been following several of these threads as I thought that the Quest was broken, will cross-post in hopes that I can help more folks, if I may.

I completed this Quest successfully with two different characters on the PC NA Server within the last couple weeks. The targets do spawn, but there are a few twists...

Reading several guides I noticed that they do not all agree on location. I noticed that some targets were easy and right where I expected, but some were killed far away from where I was told to look... always the same city but different spots. I think most of the guides are right, just targets wander a lot more then expected. As an example, Bulag (Rivenspire) was only juggling where expected once and by the time I relogged with the right character she was gone... both characters killed her when she was walking off to the east outside the castle entrance. Dinor (Stonefalls) was on the other side of the Mage's Guild and Hakida (Windhelm) was behind the bank the first time, but the second character only found her after several long nights and even then she was in the graveyard behind the Fighters Guild

The other thing that helped was that I started hunting after 23:00 MST on weeknights, when far fewer folks were playing. I really think that even with instant respawns you would have to start the search over, so they have a chance to wander more. This came to me after I had located three targets in a row woh already had a fellow assassin sneaking behind them to make the kill. Rather then interrupt I would watch the kill ad then try to go find the spawn, but that was only successful once (Alix Edette in Wayrest needs to quit moping on the docks and get out more... too easy to kill )

Again, hope this helps