Building 5 lake view does not give you a fireworks view. (although from some rooms you MIGHT be able to look off to the far side of your balcony to see a few fireworks... but I wouldn't count on it).
Building 6, some rooms may be able to see the fireworks, but you'll need to be higher up in the building. I'm not sure the 2bdrm Deluxe's would be high enough since the higher floors in that tower are all presidential units.
towers 1, 2, and 3 would be the ones with a lake view and fireworks view, again, the higher in the tower the better.
Honestly, i've personally found that the fireworks view isn't really all that great. Sure, you might be able to see some fireworks from your balcony, but the fireworks only occur for maybe 30min each night, vs. a general lake view where you can enjoy the lake in the morning before you leave to head to the parks, and at night after you return. Plus, I'm usually at the parks when the fireworks go off anyways.