Calculate base resistor of PNP transistor in switching circuit with variable resistance
The Sparkfun tutorial is very bad. The biggest mistake, at least from your point of view, is using a relatively high (75 to 100) value for beta.

Because the transistors are being used as switches, they must be over-driven compared to "regular" linear amplilfier use. This is called being in saturation. The rule of thumb in such cases is to assume a beta of 10, since this will produce very low (0.1 to 0.2) voltages for modest current levels.

In your case, your 50k pots will limit the collector current to such low levels (65 uA or so) that in principle you only need base resistors on the order of 500k. However, at these low levels you'll start running into leakage problems.

You're probably better off replacing your pots with 1k units with 100 ohm limiting resistors, and using something like 10k base resistors.