I've been playing ESO seriously for half a year now, and love it. Generally speaking, the writing quality in quest lines is very good and as a (mostly) quester that makes me very happy. However, the sheer amount of plotlines, the dividing of some of the said plotlines into different alliances and the fact that all one player's characters share a bank and thus must exist in the same "time-space" do create quite a few narrative problems for anyone who cares about such things. Unfortunately, I do care to a point. So, there has to be a way to explain how it is possible that different characters can do the same plotlines. Some of the ways could be (listed in the order of seriousness):
1. How can different characters complete the same questlines, even though they logically obviously could not (because only one of them would be able to)? Of course, one could just complete one questline woth only one character, but that would create its own problems. E.g. it would be a major plot hole if with one character cleared Velyn Harbor, but with another one who comes there later it would be in the hands of the invaders still (and remained so, because the later visitor didn't clear the town).
The solution: It could be thought that the first character to complete a quest was the only one "really" doing it. For the later ones could be argued that they are hearing the events from the first completer, and are putting themselves in that character's place in their thoughts. This is neat in my opinion, since the questlines rarely seem to feature choices that have very visible consequences. Most of them are of the sort that making a different choice with a later character could be construed as that character saying when hearing the tale: "Oh, you did that? Well, in your place I would have..."
Another solution is that later characters only do the quests which have the most visible consequences. For instance, I personally plan to play the alliance questlines through by every member character of the respective alliances because they alter things quite a bit. Another example of this are the quests where a whole town must be liberated in order to it become "usable", which I'll do even with a member of an opposing alliance if they have been cleared by a member of that alliance before.
2. Why do all these characters share a bank and so, obviously also space-time? The solution: My personal solution to this is that they all know each other at least indirectly. As an old habit, I make some kind of backstories for all my characters, so this is easy for me. For instance, my earliest four characters are members of a now defunct mercenary company, who originally made a contract to establish a common bank account with certain conditions. The rest have either met all or some of them earlier, or are friends to those who know the quartet. Anyway, the latecomers have joined the contract later via earlier members. Lately they also have decided to employ a shady Dunmer banker as a convenient go-between.
3. How can Nuzhimeh and Tythis always be there when you need them, even though they can have just a moment ago been seen by another character the whole continent away? The solution: This one's easy. Either they are secretly also mages able to use teleport magic (and an alert system for customers in need), or disguised Daedra. This is more of a question if the player characters would want to know...
4. Of course, all of the above could be explained away by a dragon break or some other freaky time metaphysics stuff in which the Elder Scrolls lore seems to find delight. Or, if we are to be really boring, by "duh, it's just how the devs decided the game mechanics should be!". But where would be the fun in that?
Any other potential logical holes anyone has spotted? It would be interesting to hear how others think of these.