No COD yet - no ID of remains yet for that matter. Yes there was land for sale. I think they made known they had money on them one day and were followed therefore the next day by someone who had heard, or overheard. If we posit drug-taking - drugs do tend to make one incautious at times, especially meth, which causes one at times to feel invulnerable. And no, I don't think they walked where they were found. (Or found evidently, pending ID.)
Although my experience with drug users is limited I'll share my opinion. The Jamison's behavior certainly suggests a dysfunctional family and drug use. They appeared to have no visible source of income, yet they reportedly traveled to Mexico and a number of other States to spend time in their time share properties. People with mental problems such as Mrs. Jamison frequently self medicate with drugs in addition to their prescribed drugs to cope with their problem which almost always worsens the situation. Assuming that Mr. Jamison was seriously disabled with a broken back we can also assume that he took or was taking pain medications. Unfortunately, this frequently leads to an addiction to narcotics. Obviously, LE will have information on this subject that has not been made available to the public.
Based on their behavior and medical history my guess is that there is a high probability that they were regular users of drugs although the drugs did not necessarily include meth. It is more difficult to form an opinion as to whether they were meth users. In many ways they acted like meth users, but in many ways they didn't.
The things that suggest that they were not completely consumed with meth use are the following. 1 They managed to hold on to $32,000 cash; 2 I have not read where anyone has said that they have seen the Jamisons use meth or admit that they have used meth; 3 They owned a home and time share properties; 4 They managed to conduct family business; 5 There has been no report of finding any meth or meth paraphernalia among their possessions; 6 They apparently attended church at times.
If they were meth users, it is my opinion that they were not yet completely consumed with it. Generally speaking, thoroughly addicted meth users who are not independently wealthy cannot hold on to any cash, someone always knows of their use of meth, they don't own much property of any kind because everything gets sold to buy meth, they are unable to conduct family business, and there is some evidence of meth use such as needles or other paraphernalia, and they don't go to church.
The above is my opinion based on what I have read up to this point in time. If a reliable source told me today that they were in fact hard core meth users, I would have to say that I'm surprised that they were able to function as well as they did. Maybe the forensic examination of the bones will reveal the answer.