Hi,
I'm attempting to replace a dual switch with a dual switch and receptacle. There are three wires running into the box (one black, one red, and one yellow). These three wires are the only wires in the box. They run directly to the dual switch but nothing is running away from the switch. One switch operates a light above a sink and the other operates a ceiling light. The sink light can be on while the ceiling light is off and vice versa. Both can also be on or off at the same time. I'm unable to make sense of the wiring and how to replace the switch if it is even possible.

Is it possible? If so, how can it be done?

Oh, another complicating factor is the dual switch receptable I bought is a GFCI. It has three wires coming off it (one black, one white, and one yellow.)

Thanks in advance.
Ron