I have to laugh. As the two litters get more exposure, the easier it gets for them to open up to all sorts of possibilities. This conditioning business works.
It doesn't stop either when they go to their forever home. This should be only the start.
Tonight Spice goes to class. Sure she learns but she also gets exposed to dogs leaving from the class before hers and the big dawgs in her class.
By doing it this way, you expose in a safe way and it becomes natural.
It's never too late or too old to take a class or two.