A brave 8 yo can ride everything at WDW. We just got back and my 7 yo rode everything except tower of terror. She was tall enough, just not quite brave enough.
A parent who does not like jerky rides should avoid big thunder mountain railroad, space mountain, dinosaur, startours. I can't think of anything else off hand that would be a problem at the WDW parks you listed. For more info on seaworld, check out the orlando attractions board.