Are The PvP matches that I observe actually being played?

I recently came back to Guild Wars and one of my favorite things to do when I am a bit busy is observe games, however one thing has always nagged me, how can these people possibly play so long? They are in multiple matches for hours on end. Are the matches already played and just being replayed? Are bots on their accounts pvping for them? I am just curious because I don't understand how it works

So for the most part the matches you watch are very recent. Playing for a few hours straight isn't as unusual as you'd think.

That makes more sense, I apologize if the question seemed really obvious or something. It wouldn't surprise me if they played for hours on end but I really wondered because I just noticed the games kind of bounced around a lot with almost always the same combination of people, so I kind of wondered about botting.

I also would like to know what determines what map they play on?

*It's the same combinations of people because only matches involving top 100 guilds are recorded.
*Whichever guild has the lower ranking is the defending team, so the GvG match takes place in their guild hall.

Thank you so much for answering everything for me!

You should notice a little note saying 'Started X minutes ago' or something to that effect at the bottom of the Observe window when highlighting a match. That tells you how long ago the matches appeared on obs mode.
There is also a delay of 15 minutes before a match is shown on observer mode.

So no, you're not watching live action but a sort of recording. You can watch the same match several times.