You can do this, but be aware that you will NOT get the absolute best result this way. The scanner will optimize and balance the scan based on all four pictures, which will not be as good as if you did one at a time.
Epson's scanner software will allow you to drag a selection box over the part of the scan preview you wish to commit to a file (and other stuff of course). So IOW you'll do the scanning using Epson's software (or a third-party alternative if you wish, even the built-in Image Capture if you like). You then repeat the process of selecting and saving for the other three parts of the preview scan.
Given the number of photos you say you have, this will probably be a VERY time-consuming process. I strongly recommend you scan at the HIGHEST optical resolution your scanner is capable of (note the word "optical" there), and save your scanned originals to a lossless file like TIFF and burn the TIFFs to a DVD or CD.
With the copies of the TIFFs still on your drive, you can fix them up in the editing program of your choice and save the modified files (once you are happy with them) as JPGs for dramatically lower file size and a minimum of lossiness. Then you can "throw the TIFF away," since you have an uncorrected "original" TIFF on that backup DVD/CD you made. This will save you ever having to re-scan the material.
As I say, VERY time consuming. It might be worth your while to consider having the material professionally scanned, which often can be done for as little as $1 per picture (and they will do a better job optimizing the photo, cleaning dust and scratches etc).