Although I certainly see a good deal of 'targeting' in this case, there are doubts. Anyone who attempted to frame the McSantas would have to know of them, know a good deal about them, know a good deal about their normal routines at the holiday times and ofcourse know a good deal about the Ramseys too.
I don't think the McSantas were in fact targets of some frame job or even a half-hearted frame job to deflect attention from the real perpetrator.
I'm fairly certain that the McSantas are a bit strange and perhaps no where near what they seem to be, but that they were not pedophiles or murderers.