@Aeder you have a few misunderstandings which are somewhat important.
1. No other Spirit would tell the MC anything because they know Origin doesnt want that.
2. trust me rumours can be really destructive, especially in such a medieval time. It would mean nearly something like ruin.
Sure they can dispel them and blame the Royals but that would end up in a REALLY bad dead end. Because the Royals would (again) oppose the Spirits, which makes them unable to rule in the worst case and in the best case destabilize their country. Both things which would EVERY other country use to gain influence or even ursurp them under the pretext of removing these bad people. That would mean many dead people, destroyed land and so on. They would just make sure that the territory and fam of the MC are unharmed.
This isnt a good thing for them too, because no other noble would like that, even if they pretend to be their friends/allies. The future of the human side of the family would be very hard and full of problems.
The same is if they would go complete murdering the royals. therefore the decision of the MC isnt dumb like all people here like to call it. It is the smallest evil of all their options.
It is scary how few people are not able to see that. The only fault like I once said is that the MC would most likely try to help these Spirits and/or her parents are to overprotective.
The MC is acting like an adult, but is just lacking information about the curse and its true nature.
People who call this dumb are the ones who are the truly dumb, because they dont see/dont care about the big picture. First you all should start using your brain and think about the things that would happen if they would do what you are saying. Every action will have a reaction and if you cant completely consider that please stay silent.