Some thoughts. On/Off modulating tends to not work that well when you have a very fast rise time, that is the mixed water will rise in temp quickly when the cold is turned off. They are better for systems when you have some thermal mass, ie a radiator or bath full of water.
If the water is coming out into a basin you need to take steps to ensure that a malfunction will not dump 80C water onto your hands.
To do what you want ideally, you need proportional valves, which are motor driven. Effectively opening and closing each tap as needed, proportionally (ie 30, 40 or 80%). These can be very expensive.
I have made up simple cheap proportional valves using big ass RC model servos and ball valves (180 degrees from open to close) I have also used stepper motors, on top of standard gate or needle valves, with a fully closed limit switch to keep things synchronized.
If the mixed water is for a bath, then go with basic on/off solenoid valves, and measure the temperature in the bath.
..the only thing worse than a stupid question is a question not asked.