When are you going? Weather will play a big part and it seems like you have no wiggle room if you get stuck witha rainy or cold day.
I was there just two weeks ago and did 6 days hopping between the Disney parks and 1 day at Seaworld, and 2.5 days at Universal & Islands of Adventure.
I went during a very slow period, IMO. I had no waits for anything. Seriously. BUT...
I missed alot at MGM because of pouring rain and also , despite 3 whole days at Epcot, missed a lot of the World Showcase because of on/off rain. I also did not have time for the shows at AK. (I disagree with skipping AK...everyone told us to skip it & we (two adults/no kids) LOVED it. It is not just a "zoo". But I guess it depends on your tastes. We are both animal people.
The Day I went to SeaWorld, I was FREEZING. It was a nice park but so cold that I couldn't bear to put my hands in the water to pet the dolphins.
I wish I'd only taken a day at Universal/ IOA because we hated it with the exception of a handful of attractions. But again, we are two young adults with no children.
If you are going during a potentially cooler time of year, keep in mind that FL is not exempt from cold, and sometimes bad weather.
Do you have children? This is also something to consider. Will you be able to get them away from certain things they are enjoying or really want to go back to? I had a hard time dragging a 31 year old man away from Epcot

So much so that we altered our plans and went back to Epcot a 3rd day. I can't imagine pulling a little kid away from something to keep on a tight schedule or rushing through WDW.
I'm not trying to be too critical but I really think you should consider dropping a park or two. I agree with the earlier post about looking into Epcots Dolphin thing. I assume by the fact that you have two marine life parks planned that someone in your group is very interested in this stuff. I understand completely, as I am the same way. But have you considered maybe splitting the day between SW & DC? That way you can do them both in one day. If it's nice out and not too crowded I think you can (I'm not all that familiar with DC though).
Do you have a WDW park hopper pass? If so, I would spend more time at those parks since you are basically paying for them anyway. I know the PH passes never expire but still...
I would also seriously consider dropping Universal. Maybe go to MGM instead at Disney. That's just my opinion, but I really like MGM better. They have great restaraunts, great shows, fun rides and Fantasmic. Universal, IMO, is just not comprable at all. I don't mean never check it out ever, it certainly has some merits, but I wouldn't rush around to try and get to it when you only have 5 days.
Also, by Universal, do you mean Universal or Islands of Adventure or Both?
Again, it's hard to say without knowing who is in your group, but I really think your group shoudl read over all the particulars of the various parks and consider dropping one or two, and combining SW & DC.