We are also going with 3 generations. My suggestion is plan out trips to MK and MGM in 1/2 day segments. Do each park in the am and pm (we are planning on different days). I would suggest EE for the park for the am visit. The idea here is if anyone doesn't want to get up early, you still know you will have a 1/2 day (pm) some other day where everone can visit all together.
Everyone will have to get up early anyways for AK. And we don't do EE at Epcot because FastPass is enough for what we want to do.
This way our disney commando's are happy, and we still know we can do some shows and special rides together as a family. And no way are we thinking of keeping 3 generations together for the whole trip.