A drastic example of why nature means more than nurture can be found in serial killers. Serial killer David Berkowitz had a reasonably nurturing childhood, no more or less than you most likely had, and yet he still ended up killing 6 people. This was not because of a lack of nurture, but his natural predisposition towards psychopathic behavior. Another good example is in Ted Bundy, whose most likely father, Samuel Cowell, was described as a tyrannical bully and a bigot. Interestingly, despite living with his grandparents throughout his childhood, Ted still became very violent. Nature plays the most into who a person will grow up to be, and is often as obvious as a violent parent creating a violent child despite the child never meeting him.
From what you said, those are just what some of the extreme cases are. Nurture plays part too, the example of violent child, if they are exposed to it then they will become violent, it doesn't have to come from the parent.
Some times extreme cases allow us to see the mechanisms at work more clearly. A less extreme example would be Paula Bernstein and Elyse Schein. "They both edited their high school newspapers, studied film at university, and became writers. But the identical twins didn't realize any of this until they met for the first time"(http://theweek.com...). Paula herself is cited as saying "'Since meeting Elyse, it is undeniable that genetics play a huge role " probably more than 50 percent'"(http://theweek.com...). It is highly unlikely that these twins were both nurtured into a preference for writing. It is much more logical to assume that their brains were genetically identical, and so the ability to write well was shared between the both of them making it more rewarding to pursue a career in it, causing there reunion.
In today's society, people do think nurture plays a bigger part than nature, studies have shown that, and in your case, if they live in the same environment even if they are from far apart, their environment is the cause that they both like writing.
Although in many cases involving separated identical twins the families aren't incredibly different, the families, including the ones in my example, were neutral. There wasn't an exceptional appreciation for writing in either family; it is not like the parents were writers, and in a way this makes my case even stronger because there was very little influence it seems that the families had on the twins preferences. My example shows that nature, in one of the twins own words, plays more than 90% into who a person will be.