You can learn great things about mission editing
here.
Check out this for your current problem
link :
http://www.armaholic.com/forums.php?...&p=59353#59353
My answer :
Syncronisation is not 100% trust-able,sometimes it make errors........
Just make a move waypoint where the vehicle is supposed to be waiting... in the condition.
put : unitname in thewaitingvehiclename
eg : soldier1 in thiscar1
so that the vehicle will move to next wp only when soldier1 entered it.
My Knowledge about sync...
Click WP A and drag the line over WP B and release the mouse.Now WP A and WP B are synced.
Now the important point is :
WP A ,which is the WP being clicked (the starting point of the line) is the WAITING WP.
So WP A will WAIT until WP B is activated.
so if car1 has to wait.then car1's wp will be WP A.
Good Luck,
If you feel unclear,contact me over PM.