That's true, Fergie was the only other family I could think of. I'm not convinced that Beatrice would sit down to be interviewed for the film. I've always thought she and Harry weren't as close.
At the Platinum Jubilee Eugenie and Jack were chummy with the Sussexes especially at the Thanksgiving Service, even Beatrice was laughing at something Harry said. By the week of the Queen's death and funeral, things weren't so chummy with between the Harkles and Eugenie/Jack, at least what I viewed of them in public. It's interesting if you notice Edo hasn't interacted much with Harry even at the Jubilee, when they were laughing before the church service, Edo didn't join in.
Whoever was interviewed will probably regret getting involved.