We were at WDW 3/31-4/7, saw wishes, illuminations and fantasmic.
Went to MK on 2nd last night and it was a zoo. Start of Easter crowds.
Because of the crowds it was not a great night. But the fireworks truly are amazing, especially if you have a good view of tinkerbell. We also watched Spectro (light parade) impressive, although again crowds were not great.
If you go a bit early park in a good spot with stroller, stakeout your ground, then have a treat like popcorn, lightup bracelets to pass the time.
Fantasmic is the fireworks, light, drama show at DHS, probably my husband's favorite of the week. We had dinner pkg. so were able to get okay seats without waiting forever in lineup. Our 2 and half year old liked them but I don't think I would do it with twin 18mo olds. Not sure if it would be worth it.
WE also watched Wishes from Poly, not nearly as impressive as being at the park but much more peaceful, the music is played quietly there. It was a good option for us.
Have a great trip.