I have been on a two med combo several times. I most recently was on Seroquel XR and Abilify. The pdoc weaned me off the Seroquel though because of the sedation and now I am doing well on just a higher dose of Abilify. I have taken several other combinations over the years but I don’t remember them all now.
I have only taken 2 antipsychotics together when changing from one to another.
20mg of Haldol is a lot to take everyday, you would be quite likely to get some side effects on that dose.