Most should be compatible. There is no specific requirement for Macs.
Having a webcam does not automatically mean it has a Mic. If it does have a mic in addition to the webcam, you might need to select the Mic from the Mac's Sound settings for use.
The Mac should use its own Mic if no mic is detected. It it detects a mic, then it will usually try to use that one.
If no audio is heard by the other party, check that the Monitor's mic is not muted. The monitor itself may have mic mute button.
Also, depending on the monitor, you may need additional cabling to enable the extra web cam and mic, such as USB connection or audio connection from the Mac to the monitor in addition to the video connection.
Without knowing the make and model of the monitor's it's hard to say what the issue may be.
What monitor's have you tried?