I have recently decided to do the MQ on a high level character of mine, but for some reason, none of the characters in Kvatch (Savlian Mattius and other essential guards, martin, and the priests.) have any dialogue options. They don't say "I HAVE NO GREETING," but they give no options. Characters elsewhere in the world are just fine. I'm playing on PC. Anyone know how to fix this?

Go back to the strange door, and pass thru it. If you are in the wrong world for what you want to be doing, go thru it again. Things change from cyrodiil to shivering isles, and if you use some flavor of transport that doesn't take that into account, that is exactly what you get.

Any "Main quest eliminator" mods involved here? Or diid you originally stall the MQ by just giving the Amulet of Kings to Jauffre and then ignoring the quest.

Bottom line question is what the journal thinks your progress is in the MQ. There may be no dialog options, because you logically haven't left the sewers yet, especially if you used an alternate start mod. There's probably a MQ event missing in your game that you need to complete first before they'll talk about it.

SI entry problems generally cause the "I HAVE NO GREETING" issue, so I don't believe that's happening here.

I'm using the alternate start arrival by ship mod. I have the Amulet of kings and have the quest update that I have found Weynon Priory. I just never talked to Jauffre. It seems I can't talk to him either. I'll try the SI door though.