Electrical:
Probably you can use a voltage divider with 2 or 3 resistors to divide the voltages from the battery and then use them to achieve your desired output voltages. Keep in mind the values of resistors will be responsible for the amperes flowing through.
Absolutely definitely you cannot use a voltage divider.
Servos need regulated voltage, 12V will pop them, divide by 2 at zero amps will mean well below 6V at load since a divider doesnt regulate.
The specs of those servos suggest stall current will be of the order of 3A or more.
This means at least a 6V 10A supply is needed, as well as the 12V rail (which sounds like its only
powering microcontrollers and could be 8V or so.