To answer first question: We were both parents with two children, one in CARES and one older. We booked Window-aisle-aisle-window, with the knowledge that people are always happy to switch to a better seat if it ends up being a full flight. My wife, who was sitting with the toddler, offered the window to the person ticketed for the middle and put toddler in middle and herself in aisle.
As to the second piece, I was about to write a response about why I think CARES is excluded from CRS and decided to dig a little deeper. Seems that the source of the confusion has been known to the FAA for some time now
https://www.amsafe.com/wp-content/up...n-Aircraft.pdf
Avoiding Consumer Confusion. The FAA recognizes that the term “child restraint system” was originally used to refer to child restraints meeting the requirements of FMVSS No. 213 and designed to perform effectively in motor vehicles. However, in recent rulemakings, the FAA uses the term “child restraint system” to describe any approved seat or device used to restrain children on aircraft regardless of whether or not it complies with the requirements of FMVSS No. 213. To reduce consumer confusion between a CRS meeting the requirements of FMVSS No. 213 (safe for use in motor vehicles) and a CRS designed only for use in aircraft (not safe for use in motor vehicles), the FAA has introduced a new term referring to a CRS only approved for aviation use. The FAA will call these aviation-only restraints an ACSD. Regulations regarding the use of a CRS in aircraft also apply to an ACSD. Figure 1 is an example of an ACSD (also shown in paragraph 13).
So at one point CRS excluded the CARES harness, but now includes the CARES harness...sometimes...in order to avoid confusion. Oh well.
Anyway, I think that things could be a lot clearer since some airlines have different rules for CARES harnesses than car seats. It shouldn't take reading an FAA advisory to airlines for pax to understand the rules.