Is taking tuition classes at home illegal? Is home tuition considered a commercial activity?

I stay in a two-floor apartment with six flats. My mother has been taking tuition classes in our own flat for children in 2nd grade to 8th grade for around three years. We have taken all measures to ensure the other residents are not disturbed. However, our neighbor is now harassing us to stop these classes, claiming it is illegal and a commercial activity. I would like to know if home tuition is illegal, considering that many people conduct small classes at home and the income from these classes is crucial for us. Additionally, what measures can we take against his threats? Most of the time, only ladies are at home, as my father goes to work early and returns at night. The neighbor's harassment is causing us to live in fear.