She's most likely an INTJ ^^ Which makes us seem terribly similar, although she has the classic 'emotionlessness' (or 'lack of emotion weakness'?) of the INTJ when around other people. She was the one who inspired me to start this thread because he looked up some statistics.
(Thanks for the link byt the way, it was interesting

)
I was thinking of something along the lines of nature vs nurture (which is interesting with twins, as they're usually rais in a similar enviroment and have similar/identical genes), as in the way one twin may take in upon themselves subconsiously to have the Te role and one the Fe role, similarly with Extraversion and Introversion (even though this doesn't work with me an my sister in this case).
There is also the theory that goes around saying twins are more 'psychic' than most, or it could be they usually have a better developed sense of Intuition, maybe from being raised with one another at equal ages which lead to them being able to read signs in others more effectively.
Maybe they're also more likely to be judging as they learn to discuss their ideas and come to a joint conclusion to promote fairnessand sharing in themselves and, when they're older, in others. But that could be down to being encouraged by their parents to share, maybe.
(If you understand my ramblings, you get a medal D: )