What is the ruling on money earned from renting out a guesthouse built on land for which there is no legitimate deed of ownership, and which is rented out without obtaining permits from the official authorities?

It is not a condition for the validity of a sale that it be officially documented, as a contract is formed through offer and acceptance, and writing is merely documentation. Therefore, you are permitted to benefit from the leased land, and what you have acquired from the rental is permissible if the utilization is permissible. Adhering to official conditions falls under the category of organization and public interests, and violating these does not prohibit the rental income if the utilization is permissible and without deception.