I agree. I think establishing a timeline of Alex's travels (incl. identifying the vehicles he used and who may have accompanied him) might help solve several mysteries and possible crimes, including: the whereabouts of the children, the present location of Chad & Lori (if LE doesn't already know), the attempted shooting of BB, the supposed paintball gun incident, and even AC's death (if it turns out it wasn't due to natural causes).
At various times I think AC could have been driving Tylee's Jeep, or (pure speculation) CV's truck, or possibly other vehicles. He could have been accompanied by others traveling in other vehicles. Obviously if LE clarified which possibly-involved vehicles were accounted for and which were missing, it would be helpful to WS'ers, but I can understand them wanting to keep this info close to the vest.
A few of my assumptions (trigger warning - if theorizing bothers you and you prefer to only/exclusively read about established or newly uncovered facts, I suggest you skip):
-In July I think Tylee's Jeep was at the house where CV was shot
-Around Aug 31 I think Tylee's Jeep was perhaps used by AC as one of two vehicles used for the trip from AZ to ID (as 5 people and their belongings might not easily fit into just one vehicle). If there was a second vehicle on the trip, I speculate that it could have been either CV's truck (an F 150 which remained at the house following the shooting?), Lori's Rogue, or even a vehicle belonging to AC's soon-to-be wife, who had an address in Gilbert, AZ (could she have been the "friend" on the trip?). Again, all speculation. There are certainly other possibilities for vehicles, but I do not think the second vehicle was AC's "car", as a previous thread post mentioned that AC had given his car to CR during this time.
-In September, if Tylee's Jeep, and possibly AC (though this is yet unproven) were involved in the 10/2 attempted shooting of BB in AZ, then AC had to have driven the Jeep back down to AZ sometime in Sept. It's even possible that the trip back down to AZ occurred in late Sept (after JJ was unenrolled on 9/24) and included the kids, but this is pure speculation.
-In Oct/Nov, in between the attempted shooting of BB in AZ on 10/2 and the sighting of AC "loading a truck" in ID on or about 11/26 (and keeping in mind that the Jeep was reportedly impounded in Dec in ID), someone (again, I think Alex) had to have driven the Jeep from AZ back up to ID in Oct. or Nov. Going a step further, if AC was perhaps involved in the reported paintball incident in ID on 10/9 involving TD (though as yet there's no factual basis for thinking this), it would further narrow the return trip window to between 10/2 and 10/9.
-11/26-12/12 If AC died in AZ on 12/12 (yet the Jeep was impounded in ID in Dec), how did AC get back down to AZ? After helping Lori pack "a truck" around 11/26, did he perhaps leave Rexburg at the same time as (or maybe even together with) Chad & Lori)? Did he (or they) head to AZ? While no autopsy results have been released on AC's death, his death seems suspicious to me (based on previous thread post, I thought the description/symptoms could fit a poisoning). AC may have known too much. If he was perhaps poisoned, who might have had motive to kill him?
Summarizing, if a detailed timeline of AC's travels could be established (incl. respective vehicle's), maybe surveillance footage or some other evidence could then be collected that would help locate the children and solve some of the mysteries of this case. Sorry if too much theorizing.