Hi, I am an IRL Twin.
And to answer your question: no, you wouldn't think that it's the other person while looking at a mirror. ( and you are not even the 1st person who has asked this, tho last time I was asked this I was in middle school)
I am an identical twin and I also studied psychology, if there were twins that were in this kind of relationship it would DEFINITELY be narcissitic, I mean, yuri love is already considered narc. Because we share the same body so add being a twin to that equation ^^;;
I haven't met twins who are close friends, without one trying to bully the other. I dont get along with my sister and that is super fine :3
I have read somewhere (forums) that people advice against getting married w/ twins who are too close because you will never be #1 in their lives and they will keep secrets from you or stuff like that.
Twincest is not wincest ....
This doujin had very cute art, a shame it was twincest c:
Those were my 2 cents