On the question of oxygen masks over Covid19 protection masks the EASA Covid19 Aviation Health Safety Protocol has this to say;
Aeroplane operators should include in their safety demonstrations that, in case of emergency, passengers should remove their face masks before using the aircraft oxygen masks. Furthermore, aeroplane operators should instruct their crew members to remove their protective face masks in case of emergency, in order to facilitate the communication of instructions to passengers.
https://www.easa.europa.eu/sites/def...gers_final.pdf