I know I had the problem of deciding which vst folders to use since I have several windows (Win7 on drive C, Win10 on drive U) and wanted the vsts from both as well as others so, I created a single folder "ALLvsts" and copied the ones I wanted there and then set it up in Ableton.
Go to "Options"
then select "Preferences"
then click on "Files Folder" tab
At the bottom, click on the "Browse" button, select the folder (Like ALLvsts) or what have you.
then don't forget the button above (Use VST Plug-in Custom Folder) and set it to ON
and if necessary, click on the RESCAN button. That should do it.
If not, try existing Ableton then restart the program. You should see the instruments in Plug-ins