At this point removal of the Cylinder head is almost your only choice.
If you do manage to get is out, using an easy out and penetraiting oil and will put shavings and bad things inside the engine.
If this engine is a Ford 5.4 Triton it is easy to break off spark plugs due to the design of the spark plugs. So, a broken spark plug remover kit is available that works well. Most auto parts stores can sell you the tool.
it must have threads and create spark
The length of the metal threads at the end of a spark plug is called the "reach".
use just a little anti-seize on threads
valve stem seals
no
They are on top of the cylinder head below the coil packs. If you are replacing them it will be BEST to use Motorcraft plugs and to put anti-seize on the threads.
sounds like you have stripped the threads, if so you need a " heli coil " thread repair..and follow directions. those threads will need to be repaired or retapped,and always start the threads on your spark plugs by hand and not with a wrench.
The threads in the head may be dirty. Try cleaning them out with a round wire brush. If that does not work, try a different plug. If another spark plug will not tighten, then the threads in the head are damaged and you need them professionally repaired.
If this happens, usually you crossed the threads on the head.
If your spark plug doesn't screw in your threads might be messed up. Run down to your local Part store and ask for a Thread Chasser($arround 10$) and screw that in to your spark plug housing just as you where screwing in a spark plug. What this does is it replaces the threads. Take out the chasser, Lubricate your spark plug and you should be good to go.
that is the crankshaft sensor, it tells what position the crank is in to tell the computer when to fire injectors and spark.
With a spark plug socket, a wrench, and a small piece of hose so you dont strip out the threads upon insertion....