The leopards are the arms of Brunswick.
I think the fleur de lys arms are his own carried by the Dukes of Durrazzo since the creation of the title. They are the Angevin arms with a border for difference, the first duke being one of the sons of Charles II of Naples. If you look carefully at the roundels, especially bottom left, you can see the red label.
The Arpad arms could be there for his position at the time of painting or perhaps to show support from the Hungarian king. You can see that they are impaled with the Angevin arms. The streamer at the top of each banner shows the red label which Louis of Hungary doesn't seem to have used.
Pope Urban did lend support. This may have been moral at the time of the events of the painting, or it may have been financial and military. Soon after, Hawkwood was sent by the Pope to aid Charles. I think the crosses of St George are those of Alberico da Barbiano's company. I think the black keys on the Papal flags are probably the result of using silver on the original.
The red over black pennons are interesting. I guess these are Charles' men but I don't know their significance.
I suppose it is possible that he was using Jerusalem at this point as a symbol that Joanna had been deposed, but I think it is probably anachronistic. Strange, though, that they use Jerusalem paired with his ducal arms.
As for the distinctive haircuts, I think it is just what the well respected man about time was wearing – Charles' golden locks have the same coiffure.
link is handy for background (in Italian)