The models should be fine in TG3, even if they were originally made for TG2. The paths look OK, but it's hard to say as I don't know if that screenshot shows the *full path*. When I mentioned the path, I was not just referring to the "local" path, i.e. the fact that the image files are in a subdirectory (which is *OK*, that should not be the cause of the problem). What I was tying to determine is whether there are accented characters *anywhere in the file path*. In other words if your files are in \home\Öshyań\models\terragen\fern\ then Terragen will have a problem because it cannot handle accented characters in file paths (the O and N in my name in the path have accents). So first verify that nothing in the file path (like your name) has such non-English characters.
If that doesn't help, I would suggest simplifying the file location as much as possible and putting all model and texture files in the same folder. If there are errors on finding the textures in that case, you can relocate them using the error messages as a guide.