Guess, there is at least one conclusion that we can draw from Horry County PD contacting the Volusia County Sheriff's Office about the remains discovery; 'they do not have a body'..
The fire pit at the M's home has haunted me and imo, was likely used by them to eliminate soft tissue and other forensically indictable evidence before disposal of the remaining skeletal remains. If my memory is correct from an anthropology class attended. When a body is burned at the normal temperature range of a burn pit or campfire. The color of skeletal bones will appear very white, as would bones exposed to to direct sunlight for years..
Since TM & SM's vehicle were caught by security camera heading back to their residence and no remains were located during the search. Imo, this seems to be the most likely scenario..
Photo of human bones on a pile of burned car tires
https://www.google.com/search?q=bon...gspot.com%2F2011_03_01_archive.html;1600;1063