Retrieving library document participant count through REST

I am currently working to integrate Adobe Sign in our product, and I am struggling to find a way to retrieve the number of participants (or really any form field information at all) from a library document. The use case is we allow a certain number of signers to be selected in our frontend, which we then pass on in a REST call. The issue is, there doesn't seem to be any way to determine how many signers a template is actually configured for. Is there any way to retrieve this or even the form field data in general?