It is very frequent that meal info are wrong on airline websites (don't ask me why).
For the AF AMM-CDG, I know they list snack and breakfast but in practice it is only breakfast (which is perfectly fine knowing the duration of this flight and its timing, i.e. a night flight). You can't pre-assign seats in Y for this flight (only when flying J).
For the CDG-CVG flight (which is operated by DL), there will be lunch served bout 90 min after take-off and a snack served about 90 min before landing. For the seat selection, as the flight is operated by DL, the safest option is to go on DL site and enter your AF booking reference and you can then access your dossier and select a seat. This is valid even if you booked the flight under an AF code.

The problem you are encountering is because the booking has been made in one country and you are trying to access the booking from the AF website of another country, hence the "warning" message you got. But there is normally something like "click here" to access the booking in edit mode. Or alternatively, switch the website to the booking country site (on the top of the screen on AF website, you can select the country and the language). Doing this you'll be able to select a special meal. But again, for the seat selection on the DL-opetared flight, do it on DL website.