Generating 14V, 12V, and 5V for winbond 8051 chips such as w77e58
You might be better to use a an LM317 and resistors on the ADJ pin to select a regulated voltage that will not be unduly affected by loading.

I looked for a similar circuit, and this one from Ed Nisley's blog that also has a switch + clamp with active-high input that meets your other requirement:



It should be easy for you to figure out from the LM317 datasheet how to fiddle the resistor values and add a transistor + resistor to get the third voltage, but ask if you have any issues. Leave the 220 ohms as-is and change the other parts (R6, R7 and add one more resistor and another transistor). 

You can take the 5V regulator input from the 18V supply.