Below is a copy and paste of my reply from the thread
http://www.gofuckyourself.com/showthread.php?t=972124 regarding
clothed models. While the OPs situation in that thread is different, my response to it, and that of others, will likely be helpful in regards to your question too.
If the pictures are intended to be of a sexual nature (and/or the websites / venues they're shown in), even if no nudity, 2257 would be wise to have.
Nudity alone isn't what determines whether a 2257 is required or not, but rather the intended use of the pictures. Nudism books, such as one will find on Amazon, B&N, etc, often have no 2257s on file and depict people of all ages, including minors, in the nude.
Digress a bit, but point is that it's how the pictures are posed / intended use that determines whether one needs a 2257 ... based on what you've described, in my view, you need to ensure all models, even those fully clothed, are of legal age and have 2257s for all of them.
With all that said, definitely consult with an attorney experienced with the adult business before hiring any models, let alone shooting any content.
Ron