We are getting our passports in person at a post office.

Is there anything we should tell them about our affidavits?

The warning box on page four of the application indicates that you can attach an affidavit to the application; this will be your affidavit of citizenship evidence, even though it is not specific to this in the warning. So, the only thing that you could do is point out to the person taking your application that you are attaching your documents with your application. The warning box gives you the right to attach an affidavit.