Sure, if 2 can sleep in each queen you can get a rollaway bed for $25 extra a nite and you should be comfy. Our dd (3 1/2) slept on an air mattress our last trip.
You can do either Swan or Dolphin. I would though probably pick the Dolphin for convenience issues. Tubbi's Buffeteria is right downstairs and it's very convenient (open 24 hrs). May be easier to do breakfasts, snacks and quick meals here. Dolphin Fountain is also fun for kids. Of course, you can visit these places even if your at the Swan but obviously would be more convenient at the Dolphin. The also have refillable mugs at Tubbi's.
The grotto pool is a little closer to the Dolphin. We did just go to the lap pool when we were there (most of the time), it was quiet and easier to just sit by the steps with dd. She made some friends with some other children there.
One thing I did notice and maybe it was a fluke but we've stayed at the Swan 4x and just stayed at the Dolphin a few weeks ago for the first time. I noticed more children at the Dolphin (but this could be due to the time we were there).
Despite some of the negative feedback we had a great time there, that's why I still keep my marquee going. (honestly no trays sitting in the halls at all, CMs extremely helpful and friendly).
I'm not sure about the transferring of luggage to/from WDW resorts, you may want to check GLO's thread about the S/D or contact them directly.