After Breaking Dawn Bella turns in a baby.

They all survived.
When Edward and the rest of the family goes hunting Bella turned into a baby. Bella Swan isn't actually Bella Swan but is actually Isabella Marie, Alice Branden little sister. Years ... years ago they got spells. One spell say that Alice will be eighteen forever. The second spell said that when Bella turns twenty she will be a baby again.If they change Bella into a vampire when she is seventeen she gets all her memories back. But do she wants to have her memories or have some things remain on familiar?
How old are they really and what role they play in the things that the Cullens are vampires?