Try the breaker bar and deepwell socket, use an additional cheater bar if necessary. Take it slow and easy, maybe you'll get lucky and leave the threads in the head. Soaking it overnight with penetrating oil can't hurt either.
And yes you should torque the sparkplugs, just not to 100 ft pounds. Torque should be between 15-20 ft pounds depending on your engine.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.