I'm rather new myself so I'll just share how I make my AI units wait for each other while performing tasks.
for example I have 2 units A1 and B1 then whenever I want A1 or B1 to wait for each other to complete a task or lets say wait for each other at a certain place, I synchronize the "move" wp. Maybe I want them to attack a location from 2 different angles but I want them to attack together... so I synchronize the "move" wp of both just before their "destroy/SAD" wp's.
P.S - search around the forums as well... there's loads of info and helpful folks.