The round nut that the bigger nuts are on is pushing against the sprocket.You have to figure out how the tension is on their. Once you get it released should be easy To take off. The round nut that both of bigger ones sit on  you have to hold and then loosen the big nut as your hold the round piece once its it loose you will see a cicle clip then you pop it out and then slide axle out.  That style on their can be impossible to get off if over tighten. When I first got my durablue axle. I got to tight and had to cut it. I suggest you buy the update version of that system. Its called posi locker from durablue and will run you 75 $. I can get you a part number for it later if you need it. Goodluck.