Alexander III And Kassander Bronze.. Clean, Or Leave Be?

There's very little to clean. The patina is the actual mineralized surface of the coin. The trace of soil remaining in the recesses helps bring out detail. I'd leave them alone.

for sure avoid to do any cleaning at Alexander's coin, the patina makes it way more interesting and can't get any better
the Kassander can be cleaned very little, just enough for the legs of the horse to get connected with the body, because the patina is black the soil boosts the details
i have ruin many coins trying to learn how to clean, but what I have learn is what coins is better to leave them alone :)