Get you a wrecking bar or two, hammer, chisel, sledge hammer, reciprocating saw, circular saw, etc., drink an extra cup of coffee, get mean, and then start tearing into and cutting into any of the boards you want to replace. Pull what nails you can and drive the rest. Spiral nails are harder to pull but you may be able to get a reciprocating saw with a wood/metal combo blade (about 10 teeth per inch) and cut them off. Cut a section or two of board out and get the blade between the joist and your boards. Do it a section at a time if your must. Don't have a recip saw, then use a circular saw, or a chain saw but watch for kick backs. Good luck and post back with the results. Go back with square drive screws, either stainless or dacrotized.