If you are at the RAC counter, right at 5am, you should be able to check your bags. Be sure there are no weight issues or over sized bag issues. Otherwise, it will take longer than it should to get checked in.
For an 8:30am flight, your p/u time will be between 5:20 and 5:40. So, if it's the earlier time, be sure you are at RAC right at 5, then head directly to the bus stop. You may even want to have the family at the bus stop after dropping bags, then you can check them in and if the bus comes early, the family can tell the driver you're coming. I don't recommend doing that on a regular basis, but if your pickup time is really early, it may be tight.