The main answer you need is, there is only one voltage setting in your BIOS for ALL the DIMMs in a PC. You cannot set the voltage for each individual DIMM slot, as you proposed. You can only set all the slots to 1.5V, or 1.35V, etc.
The maximum voltage for the memory of your board/CPU is 1.65V. You can set it to almost anything lower than that, with some restrictions. In some BIOS', you can increase or decrease the memory voltage in pre-defined steps, for example 0.01V for each step. This is really not an issue in your situation.
Using memory DIMMs, sticks, or cards that match each other has become more important with each new generation of CPUs. I have mixed DIMMs from two different manufactures, and slightly different voltages, in a socket 775 board, but that would never work on a socket 1366 board, or anything newer than that. Your socket 1156 board might be in between those two, but I've never owned one so I don't know how picky they are about mixing memory. I hope all this memory is made by the same company and the same basic model, otherwise it most likely won't work together.
You MIGHT be able to run the 1.35V memory at 1.5V, or run the 1.5V memory at a slightly lower voltage, but you must check the specs for each memory type. What is the max voltage the 1.35V memory will work with? Is there a minimum voltage spec for the 1.5V memory? Can you run those two at 1.4V?
Really the best and easiest solution is simply using memory of all the same voltage, and exactly the same type. So all 1.5V, or all 1.35V, but mixing them is pure luck if it works.
Memory uses very little power really, and really should not get hot unless it's voltage is increased above it's rating.