If I book res for 5, splitting between: 1room w/ 1 adult, 1 room 1adult, 12dd, 11dd and 6dd. how will the meal credits work then if it's all one res. also 1 res is for only 3 days then dw will be bunking in with my sister to fill her room?
It sounds like the
DDP is going to make your reservations
very complicated. I'm speculating here, so your best bet is to call Disney and ask a reservation specialist to help you with this unique situation. (Other Disers might also have better advice.)
The thing that's going to give you a problem is the rule that your reservation (and associated DDP) can't exceed the maximum occupancy of the room. When your group of 5 is in two rooms there certainly isn't a problem. You can link the reservations and have a single pool of DDP credits to pull from for all 5 people. However, when you give up the second room, you can't still have 5 people on the reservation (and therefore the DDP), because your maximum occupancy is 4. (I'm assuming that since your wife will be sleeping in with her sister, the room you're keeping isn't a family suite or DVC villa with an occupancy limit higher than 4 people. I'm also assuming your sister-in-law is arriving in the middle of your trip, since you'll have two rooms of your own for only a portion of your stay.)
I think you're going to need to have three separate non-linked reservations: your two rooms together; your single room w/ 1 adult & 3 kids; your sister-in-law's room w/ 2 adults. This would mean 3 separate DDP packages and a ticket-purchase requirement for each. Ouch, that would get expensive.
A better way might be to book two rooms for the entire period, and include your sister-in-law on your reservation. You could then settle up between yourselves for the bill. This would mean that she'd be paying for more days of the DDP than she's actually using, though, because you have to buy the DDP for every person on the reservation for every night of the reservation. But you may be able to use her extra credits for signature dining or dinner shows. Also keep in mind that everyone on the reservation needs to buy identical tickets. If you were planning to get 10-Day tickets and she was only planning to get 5-Day, for example, you'd have to all get 5-Day, then upgrade yours with the extra days at a ticket window.
Or, have you priced family suites? I don't know how these are priced, but it may not be too much more expense for your family to get a family suite for the whole stay, instead of 2 rooms for the first part of your stay. The five of you could stay in your suite for the whole trip, and your sister-in-law could be alone in her room for her portion.