First check to see if they are protected. Use X-Copy, D-Copy or similar and also try with external floppy with lots of retries set. I'd also inspect the media for physical damage, like scratches..
If all fails, you could contact the guys at SPS or CAPS or whatever to help you out with original. Don't throw them away, maybe some day they could be used decoratively :-)
PS. You could connect brand new PC floppy drive as Amiga 880K, (with some modifications) maybe it would have better luck reading the diskettes..
