Definitely an addition to the collection of anecdotes.
My dad is an identical twin, and I get along with my cousins from his twin brother better than my other cousins. There's a gender / age difference with the other cousins though, so may not count for much.
Further question to the ether: Do identical twins get along better than non-identical twins?
For all its worth, I know at least 2 pairs of twins who cannot stand each other.