Quote from: mcZ on September 10, 2011, 06:13:12 PM
They wouldn't be identical if one was born M and the other was born F. 

I was sort of thinking the same thing...

Well it's actually possible.

QuoteIdentical Twins will almost always be of the same sex. There have been 3 - 5 documented cases of opposite sex identical twins. This can happen in a set of identical boys, when one twin "drops" or "looses" a "Y" chromosome, resulting in a single chromosome, or an "XO" chromosome. Without a "Y" chromosome, the twin becomes a girl with a single chromosome, and will have Turner's Syndrome.

http://www.multipletreasures.com/facts-about-identical-twins.php

Also, siblings could just be highly genetically similar by random chance.

Quote from: Billy Polo on September 09, 2011, 03:29:17 PM
I would skip the transitioning in a heart beat if I could just swap with someone.

+1. I would swap in a heartbeat too! I'm sure it wouldn't be hard to find someone to swap with!

My ex girlfriend (she's MtF) and I used to have almost the same conversation all the time, and always decided it would be to awkward.  It usually ended with me saying something like,
"We just need someway for me to give you my boobs in exchange for your penis."

Just swapping parts would be sooo much less awkward in the long run, even if it was still awkward.