Barry, I played Caroline in the same musical. I think I may be able to help you with that part. (unless you have seen the musical since your last post 6 years ago)
Caroline is based somewhat off of Ada Maria. Yet, in the musical, Caroline and Charles are only engaged, and are not yet married, yet sharing the same cabin.
She was a second class passenger in the musical (as I'm led to believe Ada is in real life). The part is somewhat small for both Charles and Caroline.
As Caroline gets into the lifeboat, everyone is singing a song called "We'll Meet Tomorrow" and towards the end everyone stops, except Charles who continues on, singing "Come say you love me as I kiss your eyes. Let one brief moment make eternal ties." Which, I guess can signify marriage.
I enjoyed playing this role and was excited to find this page, because I've recently been fascinated with Titanic, and Charles and Ada.
If I can help anymore, I'd be glad to!
-Katie