Is my money considered permissible if my employment was accepted based on mediation or favoritism from my brother and the manager, without my knowledge of their intention to deceive, especially since my work was not bribery?

Nothing is incumbent upon you, as long as you have been officially appointed and perform your work without dereliction. We advise you to increase your remembrance of Allah (dhikr), seek His forgiveness (istighfar), and be diligent in performing both obligatory and supererogatory prayers, such as Duha and Qiyam al-Layl, so that the obsessive whispers may depart from you. This is in accordance with His, the Almighty's, saying: "Those who have believed and whose hearts are assured by the remembrance of Allah. Unquestionably, by the remembrance of Allah hearts are assured."