Knights of Tezoth

I found the discussion about the Mana ability and the rebellion in towns, but I still didn't understand it

You'll have to respond with some action, for example sending a squad there to fight a battle. If you don't respond or lose, the town becomes "independent."

so he converted Osha. If they had attacked him on their turn, nothing would have happened to their town, because there are already two figures and troops there?

They would have had to fight against generated NPCs. So they strategically decided to become friends.