Don't use the action'ed way, because this will make the units
GETIN without advancing to the vehicle (imidiate getin or so).
OK, again from scratch;
Place your 4 grouped apcs and give each a seperate name;
apc1, apc2, apc3, apc4
Now create a group of soldiers and give them an ordinary move
waypoint to somewhere near the apc (not important where, but
near to shorten up boarding-time).
Into this waypoint's onActivation field you type:
"_x assignascargo apc1" forEach units this
Now add a GETIN waypoint as second waypoint for the group.
make same for the second group but off course the assign command will look now like this:
"_x assignascargo apc2" forEach units this
same for group 3 with:
"_x assignascargo apc3" forEach units this
If there's enough space in cargo, everybody should board the
right vehicle now.
~S~ CD