how do i improve the audio quality (listening & recording) of our counseling room, from the observation room?

i work in an agency that provides counseling and training in cambodia. we have a one-way mirror, 2 analog video cameras and an AKG-100 microphone in the counseling room. In Observation room, we have TV monitors, a camera switch, joystick to control the camera, and a DVD recorder. Currently I use a "karaoke-microphone mixer" (second-hand, made in vietnam?, USD18.00) to insert the microphone channel. the output of this mixer goes to DVD recorder and also to the TV (speakers). the quality of the sound is not clear(echo) - even though the volume is fine. Any recommendation on how to improve the sound quality? Huge Thanks!

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