So, imo, if SIL didnt see Bob at 130PM, let's look at the initial time line provided by JuM-
Noon or 1PM.
SIL is diligently working from around 9-after 1130AM, PB call happens, SIL leaves and Bob disappears.
Bob disappears without leaving a key for CL, who he knew was coming, without making his bed and without executing many of his customary routines in the morning. Pretty late in the morning, mind you.
So unless Bob was known to be a lay about, he must have been exceptionally tired from the previous day's heated family meeting or possibly feeling unwell. I would think.
He is dressed says SIL, assuming that SIL provided an accurate description of what Bob was wearing. He takes his keys, his wallet, is wearing his glasses (or not-wasnt there media depicting his glasses on the kitchen table?), and he leaves the house without securing the back door, but securing the front door.
The backdoor SIL says he left unlocked. Even though Bob was there when he left.
Now, how do we retro-fit the phantom SUV story? Was this car driving to and from on the wrong side of the street between 9 and after 1130AM? Because that is when SIL had the biggest chunk of time at the house to observe this, and according to the timeline provided by family, Bob was still there.