Basically,
In American civil procedure, the work-product doctrine protects materials prepared in anticipation of litigation from discovery by opposing counsel. It is also known as the work-product rule, the work-product immunity, the work-product privilege and the work-product exception.
Under the work-product doctrine, "tangible material or its intangible equivalent" that is collected or prepared in anticipation of litigation is not discoverable, and may be shielded from discovery by a Protective Order, unless the party seeking discovery can demonstrate that the sought facts can only be obtained through discovery and that those facts are indispensable for impeaching or substantiating a claim. That is, the party unable to obtain the information has no other means of obtaining the information without undue hardship.
Comparison with attorney-client privilege
The work-product doctrine is more inclusive than attorney-client privilege. Unlike the attorney-client privilege, which includes only communications between an attorney and his client, work-product includes materials prepared by persons other than the attorney himself: The materials may have been prepared by anybody as long as they were prepared with an eye towards the realistic possibility of impending litigation. Additionally, it includes materials collected for the attorney such as interrogatories, signed statements, other information acquired for the prosecution or defense of a case, "memoranda, briefs, communications . . . other writings prepared by counsel for his own use in prosecuting his client's case . . . mental impressions, conclusions, opinions, or legal theories."
However, the work-product doctrine is also less powerful than the attorney-client privilege because it is not a privilege, and therefore may be overcome by a showing of necessity.
If the PI's were hired by the family game over.
If the PI's were hired by an Attorney then the work product should apply.
To take it further as to the ownership of the tape or tape's, in my contracts it states that my agency holds control and possession of the master tapes.
Hope this helps.