Hello Danique, and great question!
Once upon a time, I frequently did the double-feature of the
firework spectacular and
Fantasmic! in one night. All though it is a challenging endeavor, it is possible. There are two options for you to consider to make this happen, and it depends on whether you decide to see the first showing of Fantasmic! or the second showing.
If you decide to see the first showing of Fantasmic!, your best bet would be to find a place to sit/stand where there aren’t too many trees obstructing the view above the
Fantasyland area. With this option, you will watch Fantasmic!, then stay there and watch the fireworks from your spot near the Rivers of America. Yes, this option means you will not be able to see the projections on the castle, but it also means not very much running around.
The second option would be to start with the firework show. I recommend finding a place to stand on
Main Street, U.S.A., that is as close as possible to the entrance to
Frontierland. Cast Members will create one-way paths before the firework show starts, so pay attention to which direction they are sending people and place yourself close to the direction you need go post-show. You may even have one of you save your spot and the other person trace the best route into Frontierland just briefly before the show starts (15-20 minutes). Once the firework spectacular is over, grab each other's hands (this is very important). The volume of movement in almost every direction can make it easy to lose someone in the crowd. So make sure to stick together with the hand-holding method. Then slowly but intentionally make your way over to the Rivers of America. You will likely not get a center view of Fantasmic!, but if there are just two of you, you can probably find some space directly in front of the
Golden Horseshoe.
Have fun -- I’m sure you will! And enjoy both shows!
Best wishes,
Lola