The electronic structure of quaternary natural minerals PbBi₂Te₂S₂ (aleksite), Pb₂Bi₂Te₂S₃ (saddlebackite), and PbBi₄Te₄S₃ (C phase) has been theoretically studied. These compounds have a layered structure: aleksite and saddlebackite are formed by seven and ninelayer blocks, respectively, and C phase consists of five and sevenlayer blocks separated by van der Waals gaps. It has been shown that all studied materials are three dimensional topological insulators with a wide band gap in the electronic spectrum and have a high spin polarization. For these reasons, they are promising for applications.