In Real Signature, the purpose of a folder is simply to organize your document templates in Real Signature. It will not group the documents within it for the purposes of sending for signatures.
If you would like to send multiple documents for signature, you will need to create a packet.
A packet is a group of documents that are sent together as one package for electronic signature. If you would like to send a Packet out for signature, you can follow these instructions: How do I create and send a packet (multiple forms) for signature in Real Signature?