Congress can subpoena witness and I believe documents as well. People are sworn when they give testimony before Congressional committees.
Impeachment is like a grand jury proceeding, although it generally takes more evidence to impeach than to indict for an "ordinary" crime, because of the political ramifications. But the trial would bee in the Senate, and since the House acts as the prosecution, they could get whatever they needed via Congressional subpoena.
Of course the 'rat Congress isn't going to do any of that. Not even if "The minority" requests hearings, IIRC, they must get the concurrence of the majority to issue such subpoenas.
Yes, Congress certainly has the power to subpoena individuals and documents, but congress, in addition to being controlled by the democrat party is an institution that is not predisposed to rock the boat. It would take some outside influence such as a court determination of lack of eligibility to force them to act.
My point is that any case filed in court must demonstrate a tangible damage and seek a type relief available to the judge before it can proceed to the discovery or hearing stage. In the event the plaintiff ultimately wins, it is the weight of a federal court ruling that would pressure the congress to act.