How ensure signers don't get completed documents.

You cannot stop a completed envelope from being delivered to the respective Recipient's DocuSign accounts (if they have one). That being said you could delay the envelope from "completing" if you added an extra process step in the workflow such as having the last Recipient be you and setting the Recipient Type to "Needs to View" so that until you actually take that "view" action the envelope would stay in process. Obviously be aware of the expiration of the envelope but until you took that final action the envelope would not be considered "completed" and hence the other Recipients would not get a final copy or show the envelope as completed in their DocuSign accounts. (it would show as "In Progress").