We will be out 3 days, 2 nights (5 meals worth of food after day 1) with 6 Adults, 2 teenagers and my little guy. We typically eat well when we go out so we will have a little more food than normal
I guess I would still have a similar question - 3 or 4 containers?
One way to look at it is to use a rule of thumb. Wild Ideas seems to (loosely) estimate 100 cubic inches per person per day. Some postings at BPL say they can do somewhat better than that, but with careful packing (which does not seem to apply to you on your planned trip). I have noted that the rule is pretty close to some experiences that Bob G has posted.
You seem to be planning at least 2.5 days for at least 8 people. That would suggest at least 2000 cubic inches, which would be your Bare Boxer plus two rented Bearikade Expeditions. Suggestion: try mocking up that space and see how it works for you.
Note that the Bear Boxer Contender is 275 cu in -- you would need about 7-8 of them if the rule is at all close. Not too surprising, since you will have 8 people, and each BB is rated for 3 days (one person).
I'm not sure how you count "little guy" and what impact "We typically eat well" will have, but the rule may give you a starting point.
Does anyone else have any comments on the 100 cu in per day rule?