FCE defaults to DV-NTSC and that's is the current Sequence you have. When any clips hit the Timeline FCE will try to connform the clips to match it's Sequence properties, in your case NTSC 720 x 480.
Also the clips are H.264 and that's not an FCE editing codec. That's why you have no video.
You can use Streamclip from Squared 5 to transcode the files to AIC Quicktime files then bring the converted files to FCE. AIC is the Apple Intermediate Codec. The settings should match the FCE Easy Setup or rendering will occur.
Select the correct Easy Setup before bringing the converted files in.
Use FCE>Easy Setup>AVCHD-1920 X 1080i60 save Project, now import the converted AIC files.
Hang on to your hat and keep fingers crossed.