There is an opportunity to connect here. Interviewees and their families may be quite happy to see the tapes curated and made available (and have input into that). But, the stories are theirs to publish or not.
That’s my assessment; it is hard to lose material or to risk losing material. But, it’s not your material to lose in this case. It’s your material to return - either as a cool exhibit/collection or as a direct return back to the interviewees/families.
I’m guessing university counsel will give you similar feedback. Another issue may be exactly how old the recordings are. That might resolve the copyright question from a legal standpoint (eventually), but the ethical issue would remain.
best,
Cam