Congress can certainly subpoena but would have to refer to the DOJ to file criminal charges. Would Barr cooperate? I don’t know.
Refusing a Congressional subpoena is ‘contempt of Congress’, which is a misdemeanor.
It requires a floor vote of the whole House.
Maybe they could testify on the Fourth of July without being sworn under oath like Hillary and her criminal cabal were able to do. Maybe they could bleach bit the evidence and smash their hard drives and cell phones. Maybe they could plead the Fifth. Maybe they could just not “recall” anything. The Democrat precedents are endless.