A: No. The installer for 3.5 includes them. Attempting to uninstall older versions will break the whole package.
Many third-party websites offer “.NET Framework 3.5 offline installers” that are bundled with adware, toolbars, or viruses. Always download directly from Microsoft.
This error means your computer already has the files, but they are disabled.
If the above link does not work, Microsoft also hosts the package on the . This is useful if you need the specific .cab file for deployment tools like DISM.
. Because these versions are layered, .NET 3.5 cannot function without the previous two. Why They Are Bundled