(These mods are more of a general solution that should reduce or minimize talking with most followers.)
I recommend using the mods No NPC Greetings and Move it Dammit for NPC Companions and Followers.
No NPC Greetings will stop NPCs from auto-greeting you or reduce the distance required before an NPC automatically talks to you or greets you. Move it Dammit will increase the distance that Companions and Creatures walk to when being "bumped", making them keep their distance from you at most times and lessening the chances of them talking to you (I wish these were real life mods).
For removal of even more annoying dialogue, also install the Shut The F--- Up mod.
I don't know of a mod that specifically reduces the Spectral Assassin's talking. About the dog, there are several solutions in this related question.