Help with auto-populating text

For the calendar the following conditions would need to be met:
1. Only 18 employees per day. After 18 we start a waiting list.
2. An entry may only be made if the name above or below (employee covering) is not already on that day from it's respective group (machine).

There are certain days that are exempt from these conditions so we would remove them from those days to allow unlimited entries. The calendar does not need to have any other information other than the name. It is simply used to let employees know that their day off has been approved.

By the way, Thank you VERY much for your help! This is definitely more than I would have been able to figure out on my own. I can certainly see an Excel class coming up for myself in the near future.

So I've been working on it and I still have along way to go but I've made a few changes. Again, thanks a ton! I'm figuring out a lot by working with what you gave me. I attached what I have so far