SR20 flight Instructor reported a ground conflict when the student landed on a runway with opposite direction departing traffic. Reporter realized afterward they had been broadcasting landing intentions on the AWOS weather frequency instead of CTAF; which resulted in other aircraft not hearing them.

Narrative

This event was during VFR day flight training with an experienced but non-current pilot getting checked out in a Cirrus SR20. Within the prior week; the student had done his Biannual Flight Review (BFR) & Instrument Proficiency Check (IPC) within this type of plane. I was assigned to evaluate and instruct the student on partial panel approaches; various emergencies and simulated power off landings as part of his final checkout to rent the Cirrus SR20.Due to the COVID-19 pandemic; I am a former airline pilot working as a Certified Flight Instructor (CFI). At the time of this incident; I had about 60 hrs in the Cirrus and about 40 teaching in it. I previously had over 1;000 hrs of experience working as an active CFI about XX years prior. This was a factor; because I previously taught in State which had significantly less air traffic than the east coast.I planned to do a simulated engine failure over ZZZ as part of our training. Prior to pulling back the power; I set up the AWOS and Unicom Frequencies for ZZZ. I also used the ADS-B and visual scanning of the field to verify no aircraft were in the pattern. I did visually see two aircraft taxiing out toward the runway.My student monitored the AWOS at ZZZ in preparation for an anticipated practice instrument approach. I pulled the power back about 3;500 ft. AGL and just past the field; simulating an engine failure. I began broadcasting my intentions about a simulated engine failure into what I thought was the ZZZ CTAF. I heard weather from the AWOS; but assumed my student had not turned off the AWOS in the other COMM radio due to handling the emergency so we heard the weather in our headsets during the entire maneuver. I was ACTUALLY broadcasting about the simulated engine failure maneuver on the AWOS frequency. What added to my certainty I was on CTAF was that another aircraft actually responded to us inquiring about the simulated emergency maneuver using the AWOS.The winds were fairly light; and ZZZ has a very long runway; so my student opted to set up the simulated emergency approach with a light tailwind rather than using the active runway of XX. Because I was in a checking; rather than teaching role; I allowed the maneuver to continue assuming that other traffic was advised and no one was currently in the pattern; plus I was making numerous advisories of our intentions on the incorrect AWOS frequency. Due to the incorrect frequency; I heard no further responses.When we were on very short final to Runway XY; another aircraft lined up opposite on Runway XX (having not heard me due to the frequency issue). When we touched down; I immediately took the controls to stop and get it off the runway ASAP because I began to notice the opposite direction C-172 beginning to move.The other aircraft apparently aborted their take-off after seeing us and got off at the first taxi-way. We were about 3;000 ft. apart on the runway before both exiting.In retrospect in the future; I will always pre-brief the 'High Key/ Low Key' approach to engine failures and emphasize the importance of aligning our engine failure landings with the wind not only due to aircraft stopping advantages; but due to the huge threat of traffic when lining up on the wrong direction runway at these busy [area] fields.I will also use greater care to verify that I am broadcasting on the proper frequency when doing non-standard airwork into an uncontrolled airport.I will not hesitate to take the controls or reset the maneuver if my student is setting me up in a way that creates additional hazards.