On getting permission from people who were interviewed in a television interview, you would only have to get permission from the station that did the interview itself. Once those people agreed to be on television, they gave full rights and permissions to the station to do what they wanted with their images and sounds.
If the station chooses to give you permission to use their footage, it is the prerogative of the station itself. Just like if Matt Damon does a movie and signs over his image-release to the studio, Mr. Damon does not get to choose how the studio uses his image: whether it is for a documentary, promotions, or a scene to show on the Tonight Show.
The only people you need to get permission from are the owners and managers of the television station which owns the footage you would like to use.
