Thanks for all the suggestions. Just to report back, I did try this last night on a 3-hour concert with a lot different people playing. It actually turned out to be very good. No body complained.
Because we have a lot of people swapping between songs, the individual instruments volume vary a lot. With post-fader, I don’t need to spend much time adjusting the monitors. I only need to focus on the FOH sound which I can hear, the monitors are automatically taken care of.
I guess sometime I just need think out of the box and try something new that may work the best for me.