For starters, you might want to spell it right. Australopithecus. I've heard it pronounced aw-struh-lo-PIH-thuh-cus and aw-struh-lo-pih-thee-cus. Both of those are with a Þ as in think. The plural would be Australopitheci.

The plural of homo is homines. HO-mo and HO-min-ays.