What should the owner do if those in charge of the prayer room (zawiya) in his house refuse to demolish it for reconstruction, given that he has an official demolition order?

If you have purchased the house with a valid purchase, you have the right to dispose of it. As for the prayer corner, if those who are in charge of it have no doubt of ownership, then they are usurpers and have no right to prevent you. However, if they have a doubt of ownership, such as having bought its land without knowing your ownership, then you may give them its value as it stands, or they may pay you the value of the land and own it. Otherwise, you become partners by value. If the prayer corner was endowed as a mosque, it is not permissible to sell or demolish it. As for the official demolition order, if it is issued fairly, then it is clear. But if it is issued through crooked means, then it is obligatory to avoid that and return to justice, for the Prophet, peace and blessings be upon him, said: "You refer your disputes to me, and perhaps some of you are more eloquent in presenting their case than others. So, if I rule in favor of someone concerning the right of his brother based on his words, then I am only cutting off for him a piece of fire, so he should not take it."