Timelord Twins

Lori and Scarlett are twins, born to Amy and Rory Williams. All of their life, they have been lived in a big, blue box; but they've never ventured outside of its doors. I don't suppose they'd need to when the box is bigger on the inside and equipped with a swimming-pool, a library, a garden and everything else under the sun. But a week after their 13th birthday, their sister comes to stay. Her name is Melody, but everyone calls her River. The twins have never met her, but now she's here they're finally going to have a chance to see the outside world. River convinces their Uncle Doctor, to show them the stars, earth or at least another time-zone; turns out she's married to him and it's not like he can say no when she carries around a gun. So the Doctor takes his 'family' to the future . The three sisters, River, Lori and Scarlett, decide to ditch their parents and the Doctor and instead go to explore. But suddenly a crack opens in the ground and a bright, white light appears; eating up the three sisters. Lori and Scarlett are dumped in one time-zone; while River is dumped in another.. Amy, Rory and the Doctor are stuck where they originally were and it's time for them to find the girls, before time catches up with them and they are erased from existence.