As to Endgame's timeline, I would suspect it happened after the series, mainly because this is what folks have been saying all along. The series didn't end with Duncan dying or winning, it ended on an uncertain note, thus the movie would pick up from that.
I will admit it is POSSIBLE that Endgame takes place before the series (before the pilot episode, "The Gathering").
However, I get the feeling from "The Gathering" that Connor and Duncan have not seen each other in a LONG time (centuries?) so I would assume then that this is their next meeting (perhaps only their second meeting in the 20th century?).
I know that Methos and Joe Dawson feature in the movie. Now Methos as a character, and as an immortal is not revealed into well into the series. It is possible that he is featured, but Duncan doesn't know him yet (if it happens before the series). Joe Dawson as well, is a Watcher who is watching Duncan. Duncan doesn't meet him until a few episodes into the series, and the Watcher's aren't revealed until around that time either.
I got the impression from the trailer's and info that Dawson and Methos are known to Duncan in this movie, thus I would conclude that these take place after the series pilot.
So the possibilities are, assuming that the information about the movie being faithful to the series is not false:
1) Endgame takes place during the time period of the TV series (at least after the pilot episode "The Gathering", so at least after 1992).
2) Endgame takes place after the entire series has ended (sometime after 1998).
It would certainly be interesting if the series took place as a flashback or as an alternate take of the series.
I guess we'll really know when we see the movie (I may actually miss opening day, sadly):
If Connor or Duncan dies in this movie or if the Prize is won, we will be forced to assume that this movie was meant to conclude the story begun by the TV series.
If the movie is instead leading up to the events of "The Gathering" (example: Duncan goes away to Seacouver to live with his new love Tessa, and Connor goes hunting after some Immortal named Slan Quince, etc.) then we'll know it takes place before the series.
If the Kurgan is still alive, we know that it takes place prior to the first movie.
The thing to remember is that each movie can get a bit confusing if you don't see the whole thing (or the series, etc). We won't count flashbacks. So let's review:
"Highlander"
takes place in 1985 and 1986 (flashbacks to the 1500's and 1783)
"Highlander 2: The Quickening"
takes place in 1999 and 2024
(flashbacks to '500 years ago' on the Planet Zeist)
"Highlander 2: The Renegade Version"
takes place in 2024 (flashbacks to 1999, and a "a very long time ago")
"Highlander III: the Sorceror/Highlander: the Final Dimension"
takes place in the 1590's and 1994 (with flashbacks to the 1500's of the first movie period, and the late 1700's).
As to Connor and Duncan's swords, take a look at the official site:
http://www.highlanderendgame.com) There are a few details showing both of their sword handles. Now tell me they are the same. ; )
Also, if you look at just about any sword catalouge, you'll see that their swords are different. (ie: US Cavalry, Museum Replicas Unlimited, the Noble Collection, etc)
Kurgan