How do i spawn multiple robots in gazebo

edit

I want to spawn multiple robot in a gazebo world but if I spawn more than one Robot Gazebo crashes.

The launch file:

def generate_launch_description():
with open("environment_vars.yaml", "r") as stream:
    try:
        environment_yaml = yaml.safe_load(stream)
        print(environment_yaml)
    except yaml.YAMLError as exc:
        print(exc)

ld = LaunchDescription()
use_sim_time =True
for n in range(4):
    namespace="rb"+str(n)

    robot_xml = xacro.process_file(
        os.path.join(
            get_package_share_directory("rb_theron_description"),
            "robots",
            environment_yaml["robot"]+".urdf.xacro",
        ),
        mappings={"prefix": environment_yaml["prefix"]},
    ).toxml()

    declare_robot_model_cmd = DeclareLaunchArgument(
        "robot_name",
        default_value="rb_theron",
        description="name of the robot in the simulation",
    )

    start_robot_state_publisher_cmd = Node(
        name="robot_state_publisher",
        package="robot_state_publisher",
        executable="robot_state_publisher",
        output="screen",
        parameters=[{"use_sim_time": use_sim_time}, {"robot_description": robot_xml}],
        remappings=[('/tf', 'tf'), ('/tf_static','tf_static')],
    )
spawn_robot_cmd = Node(
        package="ros_gz_sim",
        executable="create",
        output="screen",
        arguments=["-name",
            "tb_"+str(n),
            "-topic",
            "robot_description",
            "-z",
            "0.2",
            "-x",
            str(-2+-2*n),
            "-y",
            "0",
            "-Y",
            "0",
        ],

    )    

    group = GroupAction([
        PushRosNamespace(namespace=namespace), 
        declare_robot_model_cmd, 
        start_robot_state_publisher_cmd,
        spawn_robot_cmd,
    ])
    ld.add_action(group)

return ld

The error Message from Gazebo:

I use ROS2 Humble together with gazebo garden.

Thanks all