Hi xorisa,
1. I have not encountered this situation before. It seems that the two charts are actually the same, so your changes to one will affect the other. But if you create charts normally, each chart must be independent.
2. Yes, it is supposed to happen. There is no binding relationship between a view and a chart. You can see any chart of this entity on any view within an entity.
For example, the Case entity already has 5 charts, and then I created a new view for Case, then you can see the existing 5 Case charts on this view.
Moreover, if my answer helped you, please click Yes under "Did this answer your question?". Thanks.