Once those clowns mature, pair up and start breeding they won’t want any fish near their turf, and their turf will likely be the whole 29g tank. Once in breeding mode they will most certainly kill any firefish. The flame angel should hold it's own but unless you can set up nice hiding spaces on either side of the tank they will have issues.
Some clowns are more aggressive then others, but even percs or false percs will feel like they have to protect their space once they start to breed. Skunks are about the most docile where clarki, maroons and tomatoes are on the more aggressive side, leaving percs and saddles in the middle of the pack when it comes to aggressiveness.