Does the reward for acts of obedience that I perform as a guide diminish due to others' envy when they become aware of these acts? And do the two surahs of al-Mu'awwidhatain protect one from envy, by Allah's will?

Envy is real and can, by Allah's permission, cause blessings to vanish. However, one should not be overly scrupulous about this matter. It is sufficient for a servant to adhere to showing gratitude to Allah, obeying Him, and reciting the Mu'awwidhat (Surahs Al-Falaq and An-Nas) for protection from the evil of the envious. Scholars have not stated that the envious eye affects a person's abandonment of obedience. Therefore, one should conceal one's good deeds and not disclose them unless there is an overriding benefit. So, beware of abandoning obedience for fear of envy.