There is so much to do at WDW and US that it can truly be overwhelming. I must say that my 2 sons (8yo & 10yo,) have enjoyed all of it, and loved staying at Universal HRH last year and spending alot of time at IOA and US. I think both your 8yo and especially the 19yo would like these parks. The lay-out of both parks and City Walk all being together make it easy to get to both parks. It's the getting out of a park once you get in that make it hard-because there is so much to do.
Wilderness Lodge 2000
2001
2002
Hard Rock Hotel 2003
Hotel up in the air 2004
Good Luck, whatever you do, and most importantly, schedule time at the hotel for relaxing and swimming. Don't feel like you have to do it all. Enjoy your time!