You can book different packages and not pay for things twice. You did not say how long you are staying, if more than 7 days, I would tell you first to look at annual pass even for just one adult because the room discount can save you lots.
Say you are staying 7 nights the first four alone, the last three with parents.
You can book a package for your family at AoA, with dining and tickets. You can then add days to the tickets and not have to book a whole new package at say SSR 2 bedroom when parents come, saving you enough money to pay for food out of pocket.
SaY you do it the other way and parents come first, you would have there dining and yours, say they use some but not all, and you stay 3 days longer than they do, you would have those three days to use there credits also, so you could do lots of 2 credit restaraunts during those three days, like Cinderella royal table and such. Credits are booked but not to a specific person, but those using it would have to be in same chatagory, so a Disney adult which includes a child over 10, can use grandmas points, not a child. At able service, I guess quick service does not matter. We had a ton of left over credits one year and we used them for 2 credit restaurants. We went with a Disney college worker, and she had to work a lot but rule is we had to have her on dining so we did, with the extra we used them for hoop de doo, and mickeys Backyard BBQ, and such, the quick service we used to get some extra soup, or oatmeal for morning for the baby who was just under three and did not have a dining plan.
Hope that helps.