Jasper; was kidnapped from a war age 7 then was with gang leader Maria for 6 years being an unpaid assassin taught only to kill other gangs. A charity found out about it and got him out of it. He met Alice in the charity and the Cullens adopted them when he was 13. Although he had developed a conscience and is trying his best to change and is now a fully recovered apart from when he sees blood as it reminds him too much of his old life. He has been with them for 5 years.
Alice; was stuck in 1 of the few asylums left as she had very good foresight she was considered a witch. She was put in there age 11 and stayed 2 years before the charity got her out. She met Jasper and it was love at first sight. The Cullens adopted her & Jasper when they were 13. She is the main reason Jasper is coping with the life swap. She has been with them for 5 years.
Rosalie; was a local well known beauty queen and she lived on the praises until 1 night her long time boyfriend Royce (18 at the time) who she was expected to eventually marry attacked her when she was 13. She was well known to the Cullens before and when it became apparent her parents did not care the Cullens took her in. She is now firmly with Emmett. She has known them for 8 years and lived with them for 7 years.
Emmett; was a normal farm worker but 1 day strayed in to the woods too far and ended up being hunted by a bear. The Cullens were passing on a road when they saw Emmett come out of the trees and Rose decided she loved him. He was just grateful to find her. He has lived with them for 6 ½ years.
Edward was the 1st addition he was suffering from a potentially fatal disease which his parents succumbed to. Carlisle was a family friend and took Edward in. He has been living with him for 9 years.