I can't answer all your questions but I can answer the first one.
I don't think there's any conflict in the two reports. They camped the nights of Monday Sept 6 and Tues Sept 7. They then "checked out" and came home on Wed Sept 8. So the camping trip was Mon-Wed or the 6th-8th. But they were camping just two nights so in that way it was a 2-day trip. Same as going to the beach for a weekend. If I check into a motel Friday night and come back home early Sunday afternoon, I'd say I was gone Friday through Sunday. But my "stay" was only Friday and Saturday.
The first link below says docs show they arrived Sept 6 and checked out Sept 8. I've seen nothing to suggest that's not what happened except sloppy reporting. Also Dog made an unverified claim early on about the trip that appears to have been wrong. He said there was proof they also camped Sept 1-3 at the same place. It appears that wasn't true. And I've seen no proof of his "3 went in, 2 came out" claim for the Sept 6-8 trip. (2nd link below)
Laundrie family changed Fort De Soto campground reservations before Brian returned home, docs show
Dog the Bounty Hunter claims to have lead on Brian Laundrie
JMO