Dang - that REALLY depends alot on their personality. You might want to find out if they are interested in anything in particular. That may spark some ideas. Also depends on wheather they are city-like or country-like. I personally like beaches. Not sure where you live, but we are by the lakeshore and that is ALWAYS an amazing place to shoot.
If they are females - im sure you want the subjects quite close to eachother at times for that warm, fuzzy feeling. Good luck!
They are seniors. What would be cool is to show them fighting between a toy (tugging at it and making varied faces such as playing that they are pissed at each other or laughing as they are tugging). Be sure they are showing as much of their faces to the camera while tugging and not moving so much that you can't see the object. An old toy from their era, if you can find one. As if perhaps they saved any? The idea of sharing always SUCKED for me as a twin.
One twin is usually more dominant than the other. You can interview them first. Make up a list of questions. For twins, mine would be:
1. Who is the more dominant of the two?
2. Who was born first?
3. What are their professions?
4. What are their hobbies?
You can draw a lot of ideas from questions you ask from people to give you ideas about your subjects in your photos of people.
I hope you post them here. I'm especially interested in seeing these! Good luck!
Are they identical twins, if so a strange question but do they still look alike?
Before you say of course they are they are identical twins, people with different lifestyles grow older in different ways.