After you post your text by pressing the save button, you press the dice icon in the top right of the post. You then scroll down and see dice commands..
Use the icon on the far left (looks like a tv remote contro), type AOO 1 into the line on the bar, then press the d20 dice icon for the 20 sided die, then press the 'then' button just below that, you'll see an option called 'add', this is where you add your to hit bonus, then roll. It's very intuitive.
Do it again for the damage roll, so with a fauchard press the d10 icon.
Repeat this for all your attacks. It's amazingly simple.
I don't get to decide if the zombies fall down, that's the DM's job. He rolls the saves for the zombies. However, if they then get up (next round) 10' from you, you get a free AOO swing (next round).