We are currently working on the custom installer for our software. And it basically comes down to the title of this topic: Is it possible to install a sub-feature, but not the parent of that sub-feature. (See picture)
I'm afraid this is the default behavior of Windows Installer.
Hierarchical relationships of parent and child features commonly exist such that if a child feature is installed, the parent feature is automatically installed as well. You can take a look on the Windows Installer Features article which may be useful.