I didn't want to start a whole new topic, so sorry if anyone has problems with me re-visiting this. Just my two cents:
Olga: Would probably read the same stuff that she did when she was alive. Les Mis, her mother's books, religious texts, poetry. She'd be described as an "old soul" no matter what century she lived in. She'd probably like a lot of indie rock, and maybe if she was in a "harder" mood she'd like Nightwish, Within Temptation, or Evanescence. She'd dress like an indie rocker/hippie chick (not a smelly, unwashed one, though), write poetry, and have the role of "angsty college student" down to a science.
Tatiana: Would be the really hot girl that all the guys wanted but couldn't have because she was out of their league. She'd dress very well, mostly designer clothes. She'd read a lot of magazines and a romance novel or book of poetry every now and then, and of course the Bible. As for music, she'd probably like whatever was popular at the time, excluding hip-hop/rap.
Maria: Would probably get married and start a family right out of high school without even going to college. Or, if she went to college, it would only be to meet guys/obey her parents. She'd dress nicely, but not as well as Tatiana (a lot more jeans and longer, more flowy skirts). She'd also probably like what was popular at the time; maybe she'd be the one into the hip-hop/rap.
Anastasia: Would be a cross between a club kid and a rocker chick. She'd probably mix and match a lot: band t-shirt with mini-skirt and pumps, sequined top with ripped jeans and Chucks. Probably wouldn't read very much, unless it was a magazine or the back of the latest Cascada CD.
Alexei: Hard to tell. When he died, he would have been too old for the traditional "kid" stuff like cartoons and Harry Potter, but not really old enough to know what he'd be into. Maybe he'd be into a mixture of hip-hop/rap culture and hard rock/heavy metal. He'd probably be like Anastasia and mix and match a lot. He'd probably play sports, too. If he were alive today, it'd be easier for him to live a normal life despite his illness.
As for Nicholas and Alexandra, I could see him being very outdoorsy (hunting and camping, sports) but also owning his own business, possibly a landscaping company or a gardening store. She would probably be really New Age-y. Long skirts, lots of beaded necklaces, crystals and tarot cards, a mixture of Enya and '60s hippie music.
I think that, if the IF were magically transported from the Edwardian to the modern era, Alexandra would have the hardest time adapting. She'd probably be appalled by all of the the above, except the psuedo-hippie/New Age persona.