Sorry, if you didn't succeed. I just tried the 3 plugins you tried to import and it worked.
I noticed a strange behavior though: when I double-clicked on a plug-in file, Windows ran a new instance of Sweet Home 3D instead of reusing the existing one. Maybe it's due to various versions of Sweet Home 3D installed on my computer, but made me think that it the installation of a plug-in seemed to fail, you should double check that you really quitted Sweet Home 3D meanwhile in Windows Task manager.