My monitor is 26 1/2 inch. I couldn't find the correct coordinates to fit my screen, since most forums are about 22-inch. Can someone please help?

Of course it's working. It's just you who are too lazy to put the required effort into it.
First you need to find out the aspect ratio of your monitor. Then choose one of the resolutions supported for that aspect ratio. If the text and characters become too small, chose a lower resolution.

I did that except it couldn't fit my screen. I tried lower coordinates, but it wouldn't work. I need an exact one it seems.
My native resolution is 1920x 1080. But when I set the coordinates for the resolution, The game cutscenes and game menus are too small for the screen.

What about the game itself? The cutscenes and menus don't scale. Some of the interior areas won't scale either.

The Widescreen mod only enlarges the main game screen properly, so you'll get a black border for the menus and cutscenes. I think there is some GUI mod you can install to fix it, though, but as long as the main game screen works properly I haven't bothered myself.
The higher the resolution, the larger the black border will be. At 1920x1080 it will be hard to read text too, so you may want to try a smaller resolution.