Mobile robots are increasingly used to automate repetitive and labor-intensive tasks in environments such as hospitals, warehouses, offices, and manufacturing facilities. When working together, multiple robots can achieve greater efficiency by sharing workloads and coordinating complex tasks, which enables faster completion of large-scale operations. Managing such teams of robots, however, requires an intuitive system for their control. This research presents a high-level graphical user interface (GUI) for controlling a group of mobile robots. The GUI simplifies robot management by providing a user-friendly interface for task assignment, monitoring and continuous control in semi-autonomous and teleoperational modes. It establishes a seamless ROS-based communication between robot hardware and software layers. The developed software was validated in the Gazebo simulator and real environment using the ArtBul mobile robot. Results demonstrated that the GUI successfully controls mobile robots within hospital and office environments, and could be further extended for multiple agents, including robots of different types, sensors and IoT-based infrastructure.