The first step you need to take is contact the travel agent. He/she should be able to take care of your flight concerns and your dining requests (If you have made them aware of your needs). You did not mention the age of your son. If you were all booked at the same time, from the same gateway city, and he is a minor there should not be a problem. If he is not a minor, you may need to use their custom air service (for a fee). If you are concerned that the travel agent has not communicated with RCI regarding your air arrangements - you can contact RCI yourself at 1-800-256-6649 (You will need your booking/confirmation number).
As for dining requests, if you get onboard and find that you are not seated at the same table, see the maitre'd. Check with the purser, but there is usually a table set up in a common area to handle all dining requests and changes before the first seating.
Finally, the question regarding gratuities: If you have prepaid your gratuities your dining room table assignment and cabin number are in the computer. Your gratuities are posted directly to the account of the staff assigned to that cabin and table. They are aware that you have tipped them. If you have exceptional service you can always choose to provide additional gratuities personally.
Hope I have answered all your concerns. Relax, and have a good time -