Well during the July 3 and 4th holiday unless you are a guest at GF, VFG, Poly, BLT, and Contemporary or have a dining reservation you are NOT allowed to enter the property. Same can apply lots of what we do not know, but when we stayed at VGF two years ago over the 4th plenty of folks are spread out and as I expect resorts will be well under capacity IMHO it's a NON issue. When we were at Poly the beaches were packed but you are also taking about 100% full resorts we are not taking about this since only DVC resorts will be open.
Still plenty of time for Disney to add and adjust things but I would not be surprised if Disney does something for guests staying on property and it could include fireworks since the parks are closed anyway.... We will know soon enough