Strange. As I see in their dialogs (ALTOS.dlg and RESAR.dlg), there are the following options:
1) You completed their sidequests, and Narlen just stabs Resar in a cutscene, everyone happy. This seems to be the only outcome depending on Narlen sidequests.
2) Resar becomes hostile, you kill Resar, Altos apologizes (which means you should be able to talk to him):
"So you've killed the Halruaan. Well, don't take it personally that I let him attack you; he was a powerful mage, and there was little I could do to dissuade him from killing you. Don't worry, you have full run of the guild—if you're able to kill a Halruaan mage, I'm sure there's little that my guild members can do to you. Again, accept my apologies for the entire incident."
In my case the second option only happens if I Ctrl-Y Resar immediately when he becomes hostile (when the game autopauses) and then the "hostility" doesn't spread through the building.
EDIT: I've just tested this in a clean BGEE installation and this works properly. Created new char, teleported to AR0153, talked to Altos, added the 3 items (MISC69, 70, 71), talked to Altos again, Resar attacks, all other NPCs do not become hostile. Resar is killed, talk to Altos, he apologizes that "there was little I could do"
So some mod is breaking that in my installation.