General aviation instructor pilot reported a near miss with another aircraft in the air and then observed the same aircraft landing with another aircraft still on the runway at a non-towered airport.

Narrative

On Day 0 I was flying the traffic pattern at Longmont; CO airport; LMO; when another plane committed two runway incursions; significantly impacting safe operations.On the first occasion; I had already flown several laps in the pattern. I was flying Aircraft X; a training airplane for our flight school. There were a few other planes also flying in the pattern. My student; a newer pre-solo private pilot was flying the pattern and making radio calls. We turned base and then final. On our final; we were on a short final (less than a mile) when I observed a plane roll onto Runway 29 ahead of us. He then paused and appeared like he was doing a short field takeoff. He made a radio call that he was departing. I recognized the hazard and knew that we could not make a safe landing. I took controls of the airplane and sidestepped us to the right (north) and had to keep nose down in order to keep sight of the other airplane. I did not want to overfly and lose sight of him and have him climb into me. He announced his callsign as 'Aircraft Y' but did not provide a full callsign. I announced we were sidestepping and overflying. One of the other planes in the pattern with us was a student solo. He was making radio calls that he was a student solo. This was Aircraft Z; a training airplane for another flight school at ZZZ. Aircraft Y ended up in the pattern behind Aircraft Z and in front of me. We flew closed left traffic and Aircraft Z completed their landing. They had been announcing they were full stop; which is common for a student solo as well. As I turned onto final; approximately 1.5 miles out on final; I observed that there were two planes on the runway. I observed that Aircraft Z was still in the center of the runway; facing runway heading; nearing the A3 exit; approximately 3/4 of the way down our 4800 ft runway. He had not turned off onto the runway exits; nor had he cleared the runway and entered the taxiway.Aircraft Y was down on the runway past the 1000 ft markers. I estimated there was less than 2000 ft distance between the two planes. Both were simultaneously exiting the runway at approximately the same time; with the Aircraft Y exiting on A2.I recognized an extremely dangerous situation; and not one that a student pilot should ever be placed in. I advised Aircraft Y on the radio he just committed two runway incursions. He responded with 'negative.' and made a comment about there being plenty of spacing.He then responded with a comment that other planes should fly a normal sized pattern. I checked the other planes ground tracks; and we were all flying a typical traffic pattern. I am still unsure if he meant we were flying too tight; or too large or a pattern. He was dismissive and took no responsibility for committing back to back runway incursions. He displayed extremely dangerous attitudes towards safety.After the student solo picked up their instructor; we then conversed on CTAF. Both of us agreed that this was very dangerous and we had both witnessed the runway incursions. We exchanged phone numbers to converse about the incident later. In addition; we agreed this was absolutely unacceptable behavior to demonstrate to student pilots. There are students training and clearly working on pattern work!That instructor; advised he would also be filing a report. He had witnessed the plane taxi but did not get the full tail number.Of note; the plane displayed only has 'VFR' on ADSB. They did not display a tail number on their ADSB. They also only used an abbreviated callsign on the radio. After the flight; I looked for the plane but did not find it. I do not know the full callsign at this time.