melgrek,
I like to stay at the HRH for my time at Universal, and stay on Disney property for my time there.
7 days will be more than enough time to do IoA, US and SW. Staying onsite gives you the HUGE privilege of Universal Express for IoA and US. Since you're going during holiday time, this is going to be absolutely invaluable!
While so many folks are waiting over an hour to ride Spider-Man, your gang will most likely ride in less than 20 minutes, often LESS. WooHoo!!
Now, that being said. Disney is going to be much less easy to navigate, since you aren't offered anything like that for staying onsite. It's a good 20 minute drive to/from US & WDW, sometimes more.
How many days do you really plan to spend in the theme parks, total?
If I only had 7 days at the time you are going, I would do 2 at Universal/IoA, 1 at Sea World, 3 at WDW.
If I had 10 days, I would do 3 or4 at Universal/IoA, 1 at Sea World, and 4 or 5 at WDW.
As for the hotel splitting, I would definately stay at the HRH for the entire time I was doing Universal's parks and Sea World. I LOVE the HRH...it's wonderful! And, since have Universal Express will spoil you to death, I would do Disney FIRST. The end of the trip will be spent at Universal breezing from ride to ride without the waits.
POR is a lovely resort. The food court is great. If you decide to spend some nights there, ask for building 14 in the Alligator Bayou section. It's the absolute closest building to the food court and the bus stop. Great location! I'm not sure if the Mansion section will be re-opened yet.