The first thing the Ramseys did was to "lawyer up".That and other things strongly suggest that they know what happened..even if neither of them actually did it.
The story that this clown in Thailand is telling is already collapsing.When the collapse is complete the case will be back at square one.
Smart (and rich) people lawyer up regardless of their guilt or innocence. It would be of no help to finding your daughter for you to be charged as the killer (which would mean that the police would stop looking for the real killer).
I thought Ed Smart and his brother were a little strange and they made some odd comments, but as I recall, the Smarts cooperated fully with the police when their daughter disappeared, and there wasn't a lawyer visibly on the scene. The Smarts didn't get railroaded into anything.