1) Well, those who pass through the gates daily would probably see a bunch of guards. Of course there's no way they'd be on guard duty all day, every day, so of course there's a rotation and of course they don't all have the same names, look the same, etc. As to which ones were involved in this particular incident, I cannot say, as I do not know. The same goes for Captain Trent. He doesn't patrol the streets 24/7 and probably gets a day off now and then. Mechanically, he's there for appearance. In "reality", he's one of several who keep to that patrol.
2) Clearly, a city like Port Hempstead has more than 2 guards and one captain. There's guards all over the place, up on the walls and so on. I believe the guards are being treated as slain. Whether they were raised or not, I do not know, as I'm not handling this situation personally. But it's safe to say that what you see in the game and what would really be in the world often differ greatly. Likewise, let's say it was the two guards represented by the floaty text that were killed. It would take a module update to rename those guards permanently. Until then, a GM might rename them after a reset, or maybe not. It's something that's difficult to change dynamically and consistently in a timely and reactive manner.
I'm certain the names of the guards will be given at the trial. Minerva is handling the event, so she will probably be the one to more completely answer these questions if my response is not sufficient.