We are a family of six with the youngest being 19. My kids grew up going to
Disneyland but two of them don't care for it anymore . . . when they got rid of Tower of Terror that was it for them, lol.
We are wanting to do a 'last' family trip before people start moving out. Originally we thought we would do Universal then it changed to Disney World and now I'm wanting to add Seaworld and Busch Gardens in Tampa.

Aarrrrgggg. I have one who really wants coasters and Disney World just doesn't have many. We aren't interested in Animal Kingdom but for sure want a day in Magic Kingdom and Hollywood Studios and possibly Epcot. I really want to do Seaworld and Busch for the coasters and the shows. But it would be nice to do Islands of Adventure and possibly Universal Studios although that looks like the least interesting of all parks to me. I am crazy?? I feel crazy.

We would be staying in a condo, have a rental car and looking at 9-11 days but could probably stretch to 12. I'm just wondering if it's nuts to try and do that much? Should we just do a couple more days at Disneyworld or try to fit Universal in? I kind of feel like if we've already paid airfare for everyone we should do what we can.
Speaking specifically to the Disney side of things, get park hopper tickets. You're traveling across the country and have a mixed group (meaning dividing and conquering will be huge for appealing to everyone). We are a family of 5 (8,6,2) and while we stayed together most of the time, on our last day we let each of the older kids pick their "I absolutely wanna ride this" options. Having park hopper,
genie+, and flexibility allowed us to really crush it in terms of riding everything we wanted, often multiple times.
Sounds like you're very experienced with "disney" so I won't lecture too much, however, I will throw this in there as possibly my biggest piece of advice.
***IF at all possible, (and I mean if there is even the slightest chance, you need to do it) you need to coordinate your Disney park days with an onsite reservation. Even if its just for 2 or 3 days of your trip. I tell everyone that will listen, early park entry is an absolute gamechanger. Just as an example: we rope dropped AK one morning, @0700, I booked our 1st genie+ for the 0850 safari tour (a time when the animals are often most active). We went straight to Avatar at rope drop, and were on the 1st group to ride flight of passage. We got off and walked straight on to Navi river journey, no wait. We then walked to the other side of the park, to Everest. We were able to ride it twice easily, and my 6 yr old even hopped on a 3rd time with his grandparents who were staying off site and had just made it through the gates. We then went to our genie+ reservation for the safari, and while on this, I made a genie+ reservation for mickey and minnies runaway railway in Hstudios. After we exited the safari, we took some picture at some of the cooler spots on the way to the exit. To recap, by 10AM, we had ridden (in my opinion) all of the must-do's at AK, and had a reservation on my favorite ride in Hstudios. By staying on site, utilizing early entry and genie+, we set our whole day up for success, regardless of what else happened, and we could let ride times genie+/LL availability etc determine how the rest of the day went. I was able to get a LL for all of us for Guardians for that evening, so we ended up spending a lot of time in Hstudios, did several shows (love the indiana jones one) and rode several things before hopping over to epcot. When we rope dropped Hstudios the next park day, there were no stressful decisions or long line waits, bcz we had knocked several things out the day before. We went straight to rise of resistance, setup rider swap, my wife rode with the older 2, and I took our daughter to ride runaway railway again. Then me and the oldest rode tower of terror while the other 3 went to toy story mania. We met back at millennium falcon smugglers run and rode it with minimal wait. I rode RoR with the boys on our way out.
***Full disclosure, your efficiency is definitely tied to your willingness/ability to put in some steps, but maintaining flexibility is the name of the game. This may not sound appealing to everyone, however, if I'm spending the time and $, I wanna get the full experience and not spend all day standing in line for 5-6 rides, that's just me.
Some other points:
- I haven't been in years, however, Islands of Adventure was always a great stop for coasters. I have heard great things about Hagrid's motorbike.
- Disney's game is more to provide a complete immersion experience than coaster style thrill, however, each park has some that I would say are very good for your thrill seekers. I'm 33 and in terms of roller coasters, all of the following are very fun.
MK: Tron, Big Thunder Mountain RR, Space Mountain
AK: Avatar flight of passage is awesome and very unique, Everest is a great wooden coaster (even better towards the front, and very neat at dusk/night), and the immersion factor is top notch
HS: Tower of terror is fun, maybe Rockin RC will finally be open someday? More of an experience based/themed park and honestly kind of light on coaster type rides, especially with the continual unavailability of its main coaster.
EPCOT: I've heard Test track is fun, chose to ride guardians 3x instead though...
Guardians is its own animal, just a completely incredible experience. Hope some of this helps.