is the motor still in the car?
through the transmission inspection hole, find a way of jamming the flywheel in place. a long thick screwdriver might even work. put a gigantic breaker bar on the crank sprocket bolt and heave on it. sometimes it helps to make the bolt slightly tighter at first in order to break the threads.
the crank hex bolts have a really nasty habit of stripping, like, all the time. in the future, make sure the hex bit is seated ALL THE WAY into the bolt by giving it a few taps with a hammer. tapping will also help break the stuck threads a little. when you go to remove it, if it feels like it's even slightly stripping, STOP turning, hit the hex bit into the bolt some more, and try again.
when you put them back in (or new ones), put some anti-seize on the threads and torque them to spec