I'm a little amused. The shy twin must be really cute if you like her that much.

Pick up lines? Why don't you just say "Hi,"? It doesn't come off too strong and she could respond to it more easily. And if she grows silent again, you could say, "You're friend told me you liked photography? Do you have a camera?" and go on from there.

Say something like that. Give her open ended questions so she can give you a longer response. This will help her relax a little while talking to you. Once she's answered enough questions, I'm sure she'll start initiating the topics in the conversation.

Take advantage of being funny, but don't try too hard.