Assalaamu alaykum. My father, my brother-in-law, and my brother, as well as a person whom I know, have made changes in their house without a permit, which is illegal. So what should I do; should I report them to the authorities, which will result in a fine of 50,000 dollars, or should they demolish the changes that they made?

All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.

The basic principle is that the person is free to dispose of his property as he wishes, by building or otherwise, and the government has no right to prevent him from doing so, unless there is a public interest in preventing that or there are negative consequences to the public if one violates the rules related to that, in which case it is an obligation to abide by the rules, and it is not permissible for a Muslim to contravene them, as this may lead to corruption and the person may be exposed to humiliation (for the contravention of the rules). Indeed, the Prophet said, “A believer should not humiliate himself.” They (the Companions) asked, “How would he humiliate himself?" He said, “By taking on a trial which he cannot bear.” [At-Tirmithi - Al-Albaani graded it saheeh (sound)]

Also, if someone enters a Western country safely and he was granted residence with some conditions, then he must respect their laws as long as these laws do not violate the Islamic Law, because the Prophet said, “The Muslims must abide by their conditions in what is lawful.” [At-Tabaraani in Al-Mu’jam Al-Kabeer - Al-Albaani graded it saheeh (sound)]

Accordingly, if what those people did violates the law, then it is not permissible for them to have done it, but if reporting them to the authorities would result in the harm which you mentioned in the question (paying a large fine), while there are no disadvantages if those changes which they made remain, then you should not report them to the authorities, and they should only seek the forgiveness of Allah and not repeat this act.

Allah knows best.