What a wonderful grandparent!
How sweet of you to say this.
I booked a room only (bounceback % off discount) last Dec. for 12/12. Last week I switched it to a package w/ dinning. The downside is that your one night deposit you paid when you booked the room only gets refunded and you put a new $200 package deposit down on the package. So if you book room only, thinking you'll later switch to a package, factor the wait for the original deposit (up to 14 days) into your plans.
To add paid for dinning as part of a package you must buy at least 1 days park ticket for everyone in the room and everyone's tickets must be the same. Note, you can change these tickets once you get there - see posts 6 and 12 in this thread for details
http://www.disboards.com/showthread.php?t=1452684
To book a package w/ the free dinning, everyone in the room must again have the same number of days and types of tickets, currently the minimum days are 2, but I believe that once you get there you can upgrade each person's ticket to what you want (you might post over in the attractions area of disboards to verify this.)
The only time you can book a package w/ paid for dinning and not have to buy the same park tickets for everyone in the room as part of the package is if 1 person in the room has an annual pass (and it only needs to be 1 person) in that case you can book the room + dinning package (no tickets) and get your tickets separately from wherever. I did this last year to take advantage of a room discount offered to AP holders.