Fantasmic is a great show. I have seen many kids younger than yours loving it but I have also seen some not so happy to be there! It can be loud, it is Mickey fighting villians so it has a bit of a dark element I guess. If your kids get scared of dark things or loud noises it might be a gamble. You can always try it and cut out if it isn't working and making them frightened. There is a scene where the lake is on fire. But it has scenes from many Disney movies projected on water screens that your kids would love. You might just explain its about Mickey fighting the bad guys and it all turns out great in the end!
As for Indiana Jones, it is a jolty, bumpy ride. It is rather dark in there. There are parts where there is fire and there is one part with a large snake that if you are sitting on the right side of the vehicle, sort of jumps out close to you. I would suggest you or your husband riding it first and deciding. Also, build your way up to that ride, for instance if Matterhorn is too bumpy and dark, Indiana Jones would probably be a no no. Haunted Mansion might also be something to test the waters on since it is dark and has some creepy parts too. I. Jones is a great ride however. My daughter was just turned 7 when she rode it the first time and loved it. She had never been to anything but a small kiddie amusement park so it was way different than anything she had done. A friend's son rode it when he was 5 and did fine, was a bit scared but wanted to ride it again! Have a great trip!