Let's be clear...It's not Rosenstein who'd be giving up documents, it'd be the DoJ. The documents aren't Rosenstein's personal papers.
What those members of Congress are attempting to do is make public information pertaining to the government's ongoing investigations into specific matters of personal import to one of their political allies. By rights, Sessions should step up and just tell Congress flat out, "When the investigation and any related proceedings in court are done, you can have all the documents you've requested, but you will not be given anything that may compromise the DoJ's ability to investigate and prosecute potential criminal activity. Period."
The notion that Congress, a body with no law enforcement authority, should have any visibility to the details of an ongoing criminal investigation is preposterous. Were they allowed to have that information, they could obtain it to advantage any political ally or even themselves, individual members of Congress.
They only asking to see Rosenstein's orders to the special counsel. There's no impropriety in asking for that. Congress has the authority to ask for proof that the investigation is legitimate. Congress represents The People and The People have a right to know.