How can I remove this valve?
While I hate plumbing, I do quite a lot for close friends and family.  I don't know exactly what you are doing, but I know a couple of things, and I hope these will help.  When you loosen the gland nut closest to the wall, you probably need to turn it clockwise.  Normally when you loosen something, you usually  go counter-clockwise.  In this case the nut stays on the pipe, not the valve.  Always you a back wrench like you were talking about to keep from twisting the pipe.

Here's a You Tube video that shows it.  I hope that this helps and is not exactly what you have done before.  Did I say I hate plumbing?