#1
I always want to play at night past 7 or 8, and two 12's at minimum volume is tone rape

So I'm wondering since the two 12's in it are two 16 ohms, that means the impedance is 8ohms right? Would i be able to unplug the two main speaker wires from my vox and plug them into the 8" 8ohm speaker?
EDIT: and the 8" is from a frontman 15, if that makes any difference to the compatibility

would i get better tone from using a smaller speaker at the same low volume?
#2
Using a smaller speaker isn't going to make the amp any quieter. The amp will still output just as much energy. Just plug a single powered monitor speaker (or even just a PC speaker) into the headphone jack and you'll get total control over the volume without any rewiring.
#3
^ Yes it will. There'll be less bass response, itll push less air, the speakers probably shittier and less efficient so it would be quieter.

No it wont sound better, itll sound a lot worse, but itll work, and dont crank the amp because i doubt the frontman speaker can handle 100 watts.

Just buy some decent headphones mate.