I found this on a site about CSA truck inspections along with lots of other pictures of acceptable tires.
Tire Inspections | DOT / CSA Insights: Success Ahead
And it clearly shows that the pictures from OP are probably legal, I think that they are carrying things too far. Even going on the premise that it's a dual, and there is another tire to carry the load, with sidwalls like this if one goes the other probably will go at the same time.
Weather checking is not a violation or an OOS condition, if the checking does not expose the underlying material.
Hank, you originally posted that this bus regularly sees long highway trips. I'm just guessing, but around here that means sports. If there is enough money in the budget for any kind of sports venue, there is enough money for tires. Many would argue with me here, but sports is NOT the primary reason for a school to exist.
I think that I would keep an eye on the situation and if the tires get replaced before the next school year, all is well. If not, even at the risk of someone getting into trouble, I think some action should be taken. Isn't someone getting into trouble better than a child getting injured or killed?