I don't think there is anything weird here. They don't want his photos to go public and as the article noted, "Saget's family has reason to believe that news and media sites are planning to file public records requests to obtain images that will infringe on the family's legitimate privacy rights, according to the Tuesday lawsuit."
It does not prevent an investigation and one already took place. They are trying to get in front of whatever fucked up media site is trying to publish them. If I were in their shoes, I'd be fighting the same battle.