I shared beds and bedrooms with at least one of my seven sisters for all of my childhood. The worst that happened to me was that I was a bit scared of going to the bathroom alone after I moved out (should have taken a sister with me). lol Of course, I learned that privacy is a wonderful thing after our three boys came along. Guess I'm trying to say your girls will grow up just fine even though they have to share! Let them enjoy it: ignore the giggling!
Mary