Is it permissible for me to work and market the rental of properties that are illegally subdivided, or to market the undivided part of the same property?

It is permissible to restrict what is otherwise permissible for a public good or to prevent a public harm. This is determined by experts and specialists. If it is for a public good or to prevent a public harm, then it is not permissible to violate it or to promote it. Otherwise, if it is not so, then there is no sin in working in it or promoting it. A believer should not humiliate himself by exposing himself to accountability and punishment. As for working and marketing in the undivided portion, there is no harm in it as long as it is not legally prohibited. Otherwise, the previous detail applies.