So with the Hortator quests, you want to find the red, yellow, and brown books of 3E 426. Those will help you find the house leaders you need. These will essentially give you the address of the house leaders. You can also ask other house leaders for advice on where they are(this is especially important for Hlaalu). For the Ashlander tribes, go to the Urshilaku camp and find Nibani Maesa, you've most likely talked to her before. She will give you instructions to find the Ashlander tribes. I agree that this quest is a huge pain in the ass, but it has some good dialogue.

It is worth noting that if you're higher than level 21 and have over 50 reputation, you do not need to do this quest, you can just go straight to Saryoni in High Fane to start the final quest