Is money earned from selling teachers' lesson plans, which my employer bought from agents after they had taken an oath, "We ask you, by Allah, the Most High, the Most Mighty, not to sell this lesson plan or give it to anyone else without our knowledge and approval, and not to publish it on internet pages," considered unlawful (haram) or lawful (halal) money, and how should I act if it is unlawful, knowing that part of my work involves other student services and I do not know the extent of their intermingling with this income?

Selling educational preparations (study guides/materials) without the permission of their owners is forbidden, because it is an infringement upon their rights and an unlawful taking of people's property. Whoever has done this must repent to Allah and seek absolution from the rights-holders by paying them their profits. If they forgive, then so be it; otherwise, it is obligatory to negotiate with them or pay the full profit. As for the workers in the office, if the office owner does not repent, then the worker must repent from participating in their sale, and it is not permissible for him to keep what he received from this sale. He must return it to the rights-holder and refrain from participating in the future. It is preferable to leave working at the office. However, if the worker's job is far removed from selling these preparations, then he is working in a place where profit is mixed between lawful and unlawful, which is disliked but not forbidden.