I think
Sidney is usable, especially with a decidedly masculine middle name like
James and the nickname
Sid. The
Sydney spelling is completely feminine to most people - I wouldn't even consider using that.
Morgan is actually used far more freuqently for boys than
Sidney, so I think that would be fine - but again, definitely use a masculine middle name to eliminate as much confusion as possible.
Mackenzie might be okay on a boy. I would stay away from
Madison - the name is so incredibly popular on girls it might be hard to picture a male
Madison. These days, even a
Madison James might be female!
Eartha sounds like the name of a tofu-selling organic foods store. Or at least it sounds like the name of the daughter of somebody who shops at a tofu-selling organic foods store. I don't like the sound, either - it reminds me of hopelessly dated old woman names like
Irma and
Bertha.
Ocean would probably work better in today's name climate, although it's not my style. I prefer Oceania - it sounds a little more "namey" than
Ocean, which to me is just a word.