https://www.justice.gov/sites/default/files/criminal-ccips/legacy/2015/01/14/ssmanual2009.pdf
b. Third-Party Consent i. General Principles It is common for several people to use or own the same computer equipment. If any one of those people gives permission to search for data, agents may generally rely on that consent, so long as the person has authority over the computer. In such cases, all users have assumed the risk that a co-user might discover everything in the computer and might also permit law enforcement to search this “common area” as well. The watershed case in this area is United States v. Matlock, 415 U.S. 164 (1974). In Matlock, the Supreme Court stated that one who has “common 20 Searching and Seizing Computers authority” over premises or effects may consent to a search even if an absent co-user objects. Id. at 171. According to the Court, the common authority that establishes the right of third-party consent requires mutual use of the property by persons generally having joint access or control for most purposes, so that it is reasonable to recognize that any of the co-inhabitants has the right to permit the inspection in his own right and that the others have assumed the risk that one of their number might permit the common area to be searched.
I don't believe the express permission by Huma and Hillary is required unless one of them took specific steps to restrict access to these documents. Manifestly, one of them could not, and there is a different case law covering it: for Clinton, the expectation of privacy disappeared the moment she transmitted an email to Huma. So the only question is: did Huma take affirmative measures to protect her privacy? If not, Matlock would almost certainly be governing.