Hi
Maybe i can help you.
I made a mission with a halo drop some time ago getting the same problem as you now. Scripts around are good, but could be better. I took the best script i found and moded it until i got what i was looking for.
Check the script i attached, i made it using a HALO script from Duma as template. I made some heavy modifications to the original script makeing it much easier.
All you have to do is to copy the script into your mission folder and then put this line into the "init" field of the soldier(s) you want to halo:
[this] exec "halodrop.sqs"
The script will take care of all the rest. You dont' have to place choppers or writing coords. Just place your soldiers there where you wanna drop them. Remember that during the drop wind will move the soldiers so place them where they can land safely (not near shore or near enemy bases).
I used this script for a long time without problems of any kind. A 5 men drop was no problem, but i never tried more than 5 man at one time. If you try that plz drop me a line and let me know.
Have fun, good luck and let me know!