changing third member

You can access the nuts through the axle flange, that's why there is one big hole in it. Use a 6" extension and a 9/16 socket and your all set.
The axle might not just slide out. If it won't and you have all 5 nuts off. Put the brake drum on backwards, put the lug nuts on so the studs are even with the top of the nuts, and use the brake drum as a slide hammer to pop the axle out.