The issue is both the boys, the Prince and even Aira herself. The boys for reason you said above, the Prince for enabling the situation despite in full knowledge that the boys action put Aira in a bad spot merely because he believes Aira being a saint deserve protections, admiration of others,... Plus his actions is based on the assumption that whatever bad rumors Aira gets everything will be forgiven and ignorable since he believe everyone should be grateful to Aira because she will save the country. Aira because she knew both what Kyle and the guys were doing put her in a bad situation but decided to not take action in fear of losing her privelege and being abbandoned if she said something that went against the Prince. She could have many occasion to say the Prince "hey maybe they aren't bad~" but decided not to. This her passiveness and decision to go with the flow despite having the opportunity to do it is also a fault and cause of the situation. (example she knows she's stuck in a low level bc the Prince had her go to low level forest... ) and mind you, soldiers were dyng on the other side. Thus she also lack the resolve to be technically a saint since despite several promises she put her situation before others and enabling a situation that just is civedo productive to her promise to work for the betterment of the kingdom. The guys acted in response to the Prince actions if they aren't being told off by him why should they stop?
i dont blame aira shes a kid that was kidnapped to a different world to fight monsters. Scared, lonely and feeling the pressure of saintess responsibility shes going to cling to the first person to show her kindness. Shes out of her element literally and I don't see her fearing losing her privileges as not taking action.
Of course no is blaming her nv she is a kid. But the matter facts is that she did allowed the situation to continue. Plus Just because she's a kid. Doesn't mean she's assolved and has no no faults for current situation. Facts are facts they don't have feelings and don't care if she's a kid or not. Reason why the situation came to that conclusion. (the prince managed to have his shitty way) a cause and effect. Also she definitely fear losing her privelege a of being taken care because she doesn't want to get kicked out. Both started in the anime/manga, novel and spinoff.
The boys surrounding the second saintess are the problem. They know their customs and how it would look to other people. The prince isolated her she really only had them so she stuck with them. The see their fiances (break up with them they knew what they were doing) hanging around her laughing and being buddy buddy. I also liked the way the anime showed her backstory. We got to see her interactions with her mom/dad they really loved her I'm sure they're devastated.