What is the ruling on taking marble that its owner has not yet removed after being warned, and disposing of it by giving it to a relative instead of destroying it? And is it obligatory to compensate its owner after a long period has passed since the incident?

It is permissible for the ruler (Wali al-Amr) to impose discretionary punishments (ta'zir) on those who violate regulations that bring benefits to people and avert harm from them. This includes the permissibility of imposing financial ta'zir, according to the majority of scholars and Ibn Taymiyyah.

Accordingly, it is permissible to confiscate goods that violate regulations. However, if you took them for yourself and did not destroy them, this is an act of aggression and usurpation (ghasb), which obligates you to guarantee the value of the marble to its owner. You must search for the owner of the marble or their heirs to return its value and seek their forgiveness. If you despair of finding them, then donate its value on their behalf. When estimating the quantity, base it on the higher amount.