The outside posts are the easiest to remove, a 4wd and or a winch will do just nicely dig a hole or shute to the side of it so it has somewhere to go and loosen up a little around the posts to reduce side friction and more so the suction cup effect.
The inside ones get more difficult where the narrow clearance becomes more of an issue. A chainsaw and cut the top half of the post off is a good way to start especially if you are useing them to prop as you go.
Back to the holes, big dark and deep, sizes of the holes will vary accordingly to your soil assessment and council submission and approvals but as a guide for an average low set house 900mm deep by 500mm in diameter would be fairly standard.
A small jackhammer can be worth its weight in gold here hardened clay and rock are common place in most areas and picking away at it with a custom made crow bar can prove long and tiresome.(for a simple custom job on the bar cut a norm in half gives you one for your mate)