During the back of head interview, I think Gannon was already about 450 miles southeast along the same route that LS would soon be driving on her way to SC. LS had placed him there in a storage facility a few days earlier, using the "airport rental" car. I think some of the extra people who were present during the interview did not take the trip to SC at all. Imo, they were there to help LS pack her things, for moral support and to say "good-bye, good luck" to LS.
Imo one of the "aunts" rented a car in her own name for LS to use for the trip.
The moving van was driven to SC by the young man using the shorter, more direct route to SC and LS drove the longer route shown on the FBI diagram. I think she used the excuse that she was going to stop in Florida and visit "a friend" for a day or so.
I think LS drove all by herself... stopped on the way to pick up Gannon and then continued on to complete the trip to SC; while leaving Gannon behind in Florida.
Here is the route she took, imo... in case you haven't seen the FBI diagram, it is attached.
This all JMO.