Were they near the glass? sometimes right after a water change and especially if the water was a tiny bit cooler than the tanks temperature, they do get the urge to breed. That is how they are stimulated to breed by the way, to do a water change with slightly cooler water. It is not unusual for them to hover near the glass finding a place to deposit their eggs as least mine did. But in the tank you described the eggs would soon be eaten. Plus you have a tank that is bordering on being overstocked.

I am sure that the fish are okay just doing what comes naturally. If you want them to spawn though they need to come out of that tank as the chance of them making a successful go of it in with those other fish will not make it.

Sounds like you really love your fish, congrats.

Rose