You don’t have to worry about extracting all of the .7z.xxx files when installing the game, Jack. When you’re extracting the game to install it, you only need to extract the first file (ERAS2.6.7z.001), and that will install the content from the other 11 .zip files. Then extract the update.zip and copy/overwrite it to your game files, and then do the same for engineupdate.zip.
Yes, Vincent is correct. If you use 7zip, and right-click to open archive of the first, #1 file, it actually opens the entire set of files for extraction. You don’t have to do them separately, one at a time.
Download them all: ERAS2.6.7z.001 through ERAS2.6.7z.012.
Make an empty folder for the game (Example C:\ERAS2) Right click ERAS2.6.7z.001, choose 7-zip/Open archive and from there, extract to C:\ERAS2). You should see in the archive, upon opening with 7-zip, modules folder, Program folder, RESOURCE folder, fmod.dll, start.exe, config.exe Buccaneer’s Reef file, start.ini, etc. Copy them all.
Unzip Update.zip and overwrite everything in that to C:\ERAS2.
Unzip EngineUpdate.zip and overwrite everything in that to C:\ERAS2