Following my OP, I fiddled around for a flying blue award booking adding AZ FF gold and trying to get Skyteam Elite Plus benefits.

Added AZ FF number through Garuda web site, as it can not be done on the FB web site or through AF phone or through FB phone. (I could not get it done despite multiple tries). The AZ number while showing on a number of Skyteam partners does not show on KL/AF/FB sites.

Changed seat through the Kenya web site:
1) normal passenger only "free" seats (seats which AF does not charge extra for selecting) are accepted by Kenya. It can not be done on the AF web site or through AF phone or through FB phone. (I could not get it done despite multiple tries and this being a Skyteam Elite Plus benefit). The on Kenya selected seat subsequently shows on AF manage booking page.
2) lap infant carrying passenger can select any seat in class for free through Kenya only, including the paid for ones. No go through AF/FB.

At online check-in the AF site does not allow to select a seat and it only shows the FB FF number. It allows to input a FF N° different then the FB one (AZ for example), but then rejects it (regardless of amount of leading "0"). It does respect the seat selected through Kenya, but you can't (I could not) select any other seat.

At the airport:
- AF accepted elite check-in. ^
- AF wanted to have me as a FB Elite Plus (AZ Gold) pay for any seat selection other then the "free" seats.
- AF did allow the extra 1 piece luggage, but sting-ed on 23.2 kg asking if I could put something from the 1st in the 2nd suitcase which was 21.9 kg. I notified them I weighed at Lufthansa before to make sure it was within 23 kg (it was) and AF didn't care, the scale you use at AF is god almighty and all other scales, even the AF colleague next, are wrong. So I luggage shuffled at the elite check-in
- AF printed a boarding pass with AZ number on, no FB number, didn't need to ask. ^
- AF refused for lap infant carrying passenger and non lap infant passengers sitting together on lap infant row as they "might" sell the infant seat row selection to someone, regardless of Elite Plus status.
- at the shared Delta/FB lounge my AZ card was frowned upon, needed to check with manager, who had to check, but was let in. Should be automatic
- in the plane, many lap infant passengers, including with newborn babies, were sitting in a non lap infant row while lap infant rows were full of "seat selecting paying" passengers without infants. In fact, the Mrs winebug was the only lap infant carrying parent on the lap infant row, and all other lap infant parents (there were a few on this flight) were scattered elsewhere throughout the plane.
- in the plane, showing both Mrs & Mr AZ Gold and kindly asking if they could seat us together on lap infant row, we were told no because the other passengers all paid for it.^
They would have put us in eco-plus which was fully booked. At least there was a positive intent.

AF execs need another public spank me thinks, this time from angry (lap infant and elite plus) passengers.