The problem is that the argument to WaitAll should be a list of your ParallelSubmit "jobs".
As in the Basic Examples of the documentation for ParallelSubmit, after first defining your function(s) and distributing the definitions, do something like:
ps = Table[ParallelSubmit[{i}, RegionPlot[f[x, y, i] > 5, {x, -10, 10}, {y, -10, 10}]], {i, 1, 2}]
Followed by
results = WaitAll[ps]