Iron forms a lavender/purple complex with salicylate ions. So it appears that the chelating agents are working. To answer your other question ferrous sulfate oxidizes fairly rapidly particularly in moist air. Ferrous ammonium sulfate is more stable but either should be OK.
I would be interested in what would happen without the chelating agents. Would be ascorbate ion be rapidly destroyed at the concentrations you used. Also the longevity of your developer with the chelating agents and iron and copper present.