Split stay 12/25 to 12/31

We are planning a surprise trip to Universal for our kids Christmas present (ds12, ds9, ds7, and dd4). We have been before and the boys all love it. We leave Christmas day evening and will be there until the 31st (2 of the kids go back with their mom on the 30th and we are considering popping over to disney for one day at MK). Right now we are staying at cabana bay 12/25 to 12/28 and Royal Pacific 12/28 to 12/29 (to take advantage of express pass) and then to the drury inn for the last two nights. I have some questions…

  1. We’ve never been to orlando at Christmas time. Are the crowds comparable to prime summer time? Will it be warm enough to swim?

  2. When transfering from cabana to royal will they transfer our luggage for us?

  3. Grocery delivery at Cabana…I’ve only even done this at WDW. Does it work the same? What service do we use? We have Amazon prime so I’m considering using prime now…

  4. Is it worth it to go to MK for one day? I know it will be crazy but something for the youngest (although we are going with her in May). I’ve never seen disney decorated for Christmas. I wanted to do the MVMCP but it ends before the 30th.

Thanks for any and all help!!!