According to the DIS, Wishes (Magic Kingdom) will be shown at 10pm and Illuminations (Epcot) will be shown at 9pm during every night of your stay. Fantasmic (MGM) will be at 7:30pm 4/3, 8:30pm 4/4 and there will be 2 showings at 8:30pm & 10pm during the other nights of your stay. Make sure to double check the official Disney website periodically before you leave as the times are subject to change.
As for seeing two shows in one night, you could probably watch Illuminations then take the monorail over to TTC then to either the Contemporary observation deck or the Polynesian beach to watch Wishes...getting into MK and positioned in time might be a stretch, but we've never tried it...transportation will definitely be an issue between MGM and either MK or Epcot.
In terms of the Illuminations cruise, you have to have special reservations. There is another thread here that has more info. (see "Illuminations Cruise Central - April"). You can also do this for Wishes. I know these are very popular so you might have trouble booking one for your dates at this point, but you might be able to coordinate with someone who already has a booking. In any event, if you can swing the cruise you would be best off not trying to see multiple fireworks shows that particular night.
Have a great trip!
