TB had left Allergan and according to a work colleague
'was excited to start his new job.'
What was this new job? We don't know. It's not mentioned anywhere except to say that he was headed for a new job/life int he Bay Area. His work colleagues don't appear to mention it as it has not been published anywhere, including on colleague's contemporaneous Twitter feeds.
That makes me curious as to what it was.
There was a farewell party at an Italian restaurant in the Irvine area shortly before the shooting.
The simplest explanations: (1) Parking both cars at one spot gives you more room for sitting/playing etc. The parking strips are made to accommodate RVs so are wide/long. (2) When you have a camping set-up, you usually unpack in the same way and that would include taking your chairs out and setting them up so that you can get the rest of your stuff out of the vehicle. TB might not know if his BIL has chairs, so he just takes out what he has as part of his normal camp set-up routine.