Last time I went into Essendon I just rang the number in the ERSA for the Security guys and they let me in and out with no issues. Just try and give them a bit of warning otherwise you may possibly have to wait a bit for them as they might be up the other end.
You don't have to call anyone if you go into Moorabbin, just type in the number written on the gate and don't forget what it was if you are heading out for a night on the town.
Find out where your friends need to go and determine which is closer to their place of visit.