Does anyone know how to make the games wide screen? I hate dealing with black bars on the sides of the screen.

Sorry, you're out of luck. They're hard-coded that way. Keep in mind a good few of these games were made when widescreen monitors weren't the norm. Avernum 6 is the only title that supports higher resolutions not dependent on a 4:3 aspect ratio.

Than I suppose the game engine is what's keeping the game from being windowed. Oh well I guess it will have to do for now.

For Avernum 4 and 5 I just let the game change the resolution on my screen.
I'm usually very picky about streched images, but it actually looks alright.
I'm on 1920x1200 though, might get too stretched on 1920x1080…

You can run Avernum 1-3 in "windowed" mode. Set that Avernum shouldn't change resolution and then choose that the game window shouldn't take the whole screen - and you have the "Windowed mode" - without system bar on top.