The "redist" is only relevant to users who do not have the game installed through Steam.
One thing that is important to know about Amnesia mods is that there's a difference between a "full conversion mod" and a "custom story".
A custom story (CS) is the most common and the way you play those is by putting them in your "custom_stories" folder as you've done already, BUT you start the game normally and then select the one you wish to play in the "Custom Story" section of the main menu.
A full conversion mod (FC) is more advanced. It offers more features than a custom story, but they have to be launched in a different way. The Amnesia Modloader only recognizes FCs, not CSs. That might be why only Tenebris Lake shows up. FCs are usually installed into their own folder as well, not the "custom_stories" folder. Usually you extract them into your Amnesia root folder, but read the instructions to be sure.
I suggest you start the game normally and see if your downloaded stories show up in the main menu. If they do, they are not FCs.
Another method to make sure what you downloaded is a CS or an FC is to open the folder for it. If there is a file called
custom_story_settings.cfg then you have a CS. If there's a "config"
folder (with a
main_init.cfg file inside), you have an FC.
Mods can be a bit tricky to install though. If you have downloaded an "isolated full conversion mod" (IFC) then it's simply put into the root of Amnesia, but not all FC mods are isolated, which means they may use odd names for folders or have multiple folders you need to extract. The reason for this is simply because there weren't proper guidelines at the time they were made. Other than being messier, FCs work the same as IFCs.