I hooked up my new 16 FSRs to the breadboard, with the original multiplexer, and new HUZZAH feather. The results from that... well.. proved that I probably need more reliable breadboards. Still, I did notice that when I pressed on the FSRs for pins 15/16, they still bled into each other. But, pin 15 was not resting at 0, whereas pin 16 was resting at zero. I also tested each FSR individually and they all work well. I believe it's just the connections in either the wires or the breadboard itself that is causing it to go a little crazy. Now I'm wondering if I have another breadboard somewhere that I lost during one of my many moves. I don't remember having this problem the first time around with testing on a breadboard.
In the end, I'm still not sure if it is the multiplexer itself that is allowing pins 15/16 to bleed, or if it is my circuitboard and breadboard that both are messing it up. Maybe the only sure thing to do is finally learn how to design and order a custom PCB for my circuitboard.
If you are looking for a summary for my Masters thesis, it is here.