I've been on many flts where the FA(s) held space in the bins above bulkhead seats in F and Y for BH pax (even bins for F are sometimes off limits to Y, but once ALL F have been seated, they let Y use the excess.)
In the "worst case scenario" there is usually space for small items in the closet near the boarding door, couldn't that have been done for these 2 pax?
I seem to have read that 2 is the MAXIMUM number of items per pax, weren't the GA(s) remiss in allowing a pax with 3 c/o's to board?
If one of the bags was medically necessary, such as a CPAP, then it doesn't count against the carry-on allowance. So you can't always tell if the person is breaking the policy or not. My CPAP is not in the standard bag because it wouldn't stay in place on the handle of my other luggage. I bought a different one that was similar in size but has a slot to slip over the handle. I always declare it at the boarding line and I don't fill it up with other stuff except maybe my baseball cap for convenience. (And when I'm in first on the aisle, I can usually get both my CPAP and my personal item under the seat.)