Hi Jennifer,
Welcome back to the Disney Parks Moms Panel! Kudos to you for making
advanced dining reservations!
I would definitely suggest that you make reservations for six people then modify that reservation later if needed. In my experience, it can be more difficult to add a person than it is to reduce the size of your party. In the past, we have arrived for reservations without certain members of the party due to illness or other unavoidable circumstances. I have not been charged a fee for those guests but I suggest that you modify the reservation as soon as you know for certain what your party size will be.
Having said that, I failed to cancel a reservation in the past and was charged $10 per person. So be sure to cancel if you change your plans completely! Also, consider your travel time carefully. We arrived 20 minutes late to a reservation once because we missed a bus and had to wait for the next one. I now allot at least an hour and a half to get from our resort hotel to a dining reservation. Luckily, the cast members at the restaurant accommodated our party despite our tardiness.
Jennifer, if you have trouble making a reservation for a party of six, try making reservations for the same time (or close to it) for a party of four and a party of two. We have done this in the past. Although not guaranteed, cast members have been able to sit our party together!
Magic, memories and Minnie Mouse hugs,
Donyell