Yes, it's possible to see both shows in the same night...the two most common methods are watching the first PtN and then see the second F! or watching the first F! and then see the second PtN. This depends a little on when you are going (which date specifically).
The "easiest" option is to purchase a dining package for F! so that you know you'll have a great view with minimal wait. Otherwise you'll have to get a FP F! and even with the F! FP viewing areas there are some areas that are better than others. The dining packages (RBT and BB) are in a ground seating-only section, so everyone should have a great view. There may be some (very limited) ground seating in the FP viewing areas, but I wouldn't count on being able to get one of those spots.
Prime PtN viewing spots for the first presention have been filling up about 2 hours before the parade steps off, so you'll have to commit a fair amount of time to waiting if you want a front row spot. With the expected increase in crowds during the holidays, I wouldn't be surprised to hear that guests are waiting for both the Christmas Parade and PtN. Usually the second presentation of PtN is less busy, but prime viewing spots will fill up almost as soon as firework ends, but there is only about an hour between the end of fireworks and the start of PtN (the second show usually starts on MS).
So it really depends on where you want to watch/see
Disneyland Forever fireworks from...assuming you aren't really interested in fireworks...I would probably aim for the first F! and then as soon as it ends starting heading to the location where you want to watch PtN. If you wait until fireworks are over, you'll probably have a harder time finding a curb/front row spot for PtN.