Applying with your uncle's information says to USAA "Myself and this other person I am giving you information about are knowingly trying to get a loan"
USAA has to assume the other person you used as a co-signer is fully aware and intended to have this loan. There is a fraud process where some bells and whistles went off based upon the information you provided. It was probably saying that the person you wanted to be a co signer was a foster parent when you are an adult. It doesn't make sense and is going to make a financial institution essentially say "what?!"
Think about it, it wasn't your intent to do so, but essentially you "lied" about your Uncles being your foster parents. That's a big deal when you get into specific legal inquiries.
If you didn't see the right relationship choice you should have called. Your dishonesty caught USAA's attention, and in a world where fraud is rampant and banks have to work very hard at combatting it, you've stumbled into an unfortunate situation.
Because USAA received your application with two applicants that it has suspicions about, they are now requesting proof of ID for both applicants (you and your uncle(s) ). It doesn't matter to them that you were just using your uncles information as a co applicant to help you on the loan, it still looks like two different people (well three based upon your multiple uncles description) are asking for a loan and USAA has to verify their identity.
The Patriot Act essentially means that USAA has to have a reasonable beleif that account holders are who they say they are. If you say your Uncle is your Foster Parent, aren't you already violating that?
At this point, you can go ahead and avoid doing anything about it and choose not to do business with them, but honestly you're missing out on what is otherwise a pretty amazing bank.