Those plugs are scrap, replace them


If jerking the clutch free does not work as described above, then you will need to access the clutch/flywheel area.

Get someone to press the clutch pedal down and if you can poke a thin screwdriver up in and try and prise the friction disc away from whichever surface it is stuck to. It shouldnt take very much effort, although you may need to rotate the engine manually and do this in a few spots to get it to break free.