Their daughter is dead; they may or may not have contributed in some manner. Your post seemed to suggest that they are faking their grief. I don't think this is the case.
Brenda turns it on and off like a light.
I am here in San Diego and have seen many of her stand up press statements. She is like a "20-20" producer, putting the cameras here, testing mikes, all business, (we see all this on live TV), then when she gets to "her statement" about missing Danielle it's all BOOO HOOO, then she talks in the next sentence about a non-sad topic like where the searchers are meeting, and she switches like a light back to all business, no tears. Sorry, it is NOT real.
Unless she has the most amazing on-off switch for her grief.