Just got feedback. EUR 600/passenger for delay will be paid in refundable voucher. Downgrade from C to PE is compensated with a CHF 200/passenger non refundable voucher. No compensation awarded for delayed luggage (which have still not yet been delivered!).

I have asked again for the 75% refund for the downgrade and compensation for the delayed luggage. Will report here.

Probably it would be harder if it was an outstation, but not being able to find a crew out of CDG until the next day is totally unreasonable for AF and as such should not be considered an extraordinary circumstance that resulted in an additional delay to the next day. The initial 2 cases of extraordinary circumstance (weather and medical emergency) does not extend exemption to the airline in the event they do not do everything within reason to prevent additional delay of a flight.

I believe this is the relevant ruling for that -- CURIA - Documents

What some airlines do to compute the 75% is to take the cost of the ticket and divide it by 2 and refund the 75%, but in some cases where it is a multi-segment flight they may also 'pro-rate' the 75% but given that CDG-MIA is the most significant sector I wouldn't settle for anything that is not close to 75% of half the price of the ticket.

To this date, I received only 1 x EUR 600 from AF. I am assuming that the non payment of the EUR 600 amount for the second passenger is the result of AF's persistent lack of organisation rather than a wilful intent.

With respect to the 75% reimbursement for the downgrade, I am being sent to claim the amount due from the seller (which is AF itself, actually).

I have also claims for much delayed luggage that remain unpaid to this date.

But to sum up, it looks like AF admitted that the statutory EUR 600 was due.

If AF continues to refuse to reimburse for the downgrade, what would be good claims' agencies?

Glad that AF admitted their liability for the 600 delay compensation.
The downgrade refund is not controversial unless there are untold parts of the story. This is technically a refund, so AF would probably refund it to whoever issued the ticket. If you personally bought the ticket online, they should refund it to you. The matter might be a bit complicated when you buy the ticket for another person. If it is bought via a TA, then the TA should probably be the one getting it. As discussed in other threads, airlines seem to have some leeway in interpreting the term "refund" and who gets the money.
Bear in mind that AF must be under a lot of work given all the recent strikes and numerous reroutings.

You now add the question of compensation for delayed luggage. Apparently the bags have now been delivered. I assume that your parents have purchased some essentials and claimed that amount. AFIK no further compensation is legally owed. A goodwill gesture of some miles is not uncommon, but you are already claiming so much, and rightly so, that I would not bet on it.

More than anything in this situation I would want my 2 days back and ask AF to push my return 2-3 days after the original return date. Then I would ask for the 600 Euro Compensation. For me I scheduled to be there for x amount of days well I do not want a shorter vacation as a result. I would even forfeit the monetary compensation if I could get a flight back to CDG in J Class or even in PE even a week or two later for the same cost. More vacation time is always nice.

I actually had a delayed flight from SFO to Europe that lasted a few days and I was flexible in my return date. I just kept volunteering my seat .So I asked the airline to extend my ticket for 3 more weeks and they honored the price and I got my vouchers and more time at my destination. Anyways as it turned out I had a family event that I really wanted to attend that was a week after my return date. So I asked the airline to just extend my ticket for 3 weeks. As it turned out I saved the change fee+Fare Difference to do this and they waived all change fees. I was happy!

Whenever there is a delay of a day or more I use it to my advantage and ask the airline to give me more time at my destination. Then I just call up the hotel/resort and ask for an extension or go online and book another property and then just tell the rental car agency about my later return date. In addition the airline gave me a Travel Voucher for $8000 due to my volunteering.

So as soon as I got the voucher in hand I booked myself another trip to Europe leaving three days after my return to SFO! When the Passport Agent back in the EU asked why I went home and came back so soon. I said I had a voucher from the airline for a delay and I wanted to return to Europe. It was amazing booking last minute luxury hotels/resorts and I did the second trip to Europe all on a whim. The entire flight was spent narrowing down my choices I booked into J Class and paid the remaining $500 to get First Class as there was a special going on.

Plus it was late September when summer crowds left.

My field is Travel Research. As an independent person I am not bound to a certain return date. I love delays as it gives me more negotiating power.