This is a tough one. The turbulence was clearly terrifying for him, and that fear needs to be addressed and dealt with. But I don't know that you have the time to deal with his fears before this trip -- as this schedule sounds rushed and timed for your parents needs, not for yours.
A trip to Disney World is something a child should have the experience of looking forward to with excitement and not dread. Part of the joy of any trip is the anticipation -- and clearly that will not be the case here.
My instincts say, postpone this trip until you have had the time to really help him work through this issue. He was obviously traumatized by the turbulence he experienced -- and this may be mixed with other fears (and possibly some additional heightened sensory issues if the noise is also truly troubling for him).
Your parents will have the time share for a long time, he will be a kid that will enjoy Disney World for a long time.
I would do research on how people work through their fear of flying (visit airports, look into videos that help people deal with this phobia) , and also possibly get some additional help as this may be related to anxiety in general. But I would not rush him through this process.
I would also find out what he is afraid of happening -- I know as an adult what I'm afraid of on a plane -- but I wonder if a five year old has those same fears or if they are different. You might also try to find out if he has been exposed to any images from TV, or films that are heightening his anxiety .
Bottom line, your child is dealing with a real anxiety/fear -- I think your instincts are telling you that you need time to address this. I would go with that gut feeling and take the time to help him through. Your parents can plan this trip with you for another time when it works for everyone