How to fix double-tapped 14-3 cable to boiler
If that is the red and black from the same 14/3 cable it is anyone's guess why they did this. In any case they are using the same circuit on both wires, obviously. If there is no problem at this time just splice the two wires to a tail of the same gauge and put that one tail on the breaker. Those GE breakers are NOT made to accept two conductors, but it's also not the end of the world either. Since you are working on it is worth fixing.

IF you do feel that stongly that you want them on separate breakers you MUST use a 2-pole breaker, and NOT a tandem, or twin, breaker.