Launching the JointGroupVelocityController

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I have some problems in launching the jointGroupVelocityController.

This was my .yaml file before:

joint_state_controller:
    type: joint_state_controller/JointStateController
    publish_rate: 50
joint_fr_motor_controller:
    type: velocity_controllers/JointVelocityController
    joint: joint_front_right_prop
    pid: {p: 10000, i: 1, d: 1000}
joint_fl_motor_controller:
    type: velocity_controllers/JointVelocityController
    joint: joint_front_left_prop
    pid: {p: 10000, i: 1, d: 1000}
joint_br_motor_controller:
    type: velocity_controllers/JointVelocityController
    joint: joint_back_right_prop
    pid: {p: 10000, i: 1, d: 1000}
joint_bl_motor_controller:
    type: velocity_controllers/JointVelocityController
    joint: joint_back_left_prop
    pid: {p: 10000, i: 1, d: 1000}

In this way, I cannot provide velocities SIMULTANEOUSLY to all the four joints. I have a .launch file that loads all these controllers, using the controller_manager pkg. This is the snippet of the controller_manager in my .launch file:

<group ns="Kwad">
    ..................
    <node name="control_spawner" pkg="controller_manager" type="spawner" respawn="false" output="screen" args="--namespace=/Kwad
    /Kwad/joint_state_controller
    /Kwad/joint_fr_motor_controller
    /Kwad/joint_fl_motor_controller
    /Kwad/joint_bl_motor_controller
    /Kwad/joint_br_motor_controller" />
    ....................
</group>

I came across the JointGroupVelocityController, that provides multiple velocities to the joints SIMULTANEOUSLY, thus I want to know how to change the .yaml file and the .launch file accordingly.

This is my updated .yaml file, but i am not sure if it's correct:

joint_state_controller:
    type: joint_state_controller/JointStateController
    publish_rate: 50
joint_motor_controller:
    type: velocity_controllers/JointGroupVelocityController
    joint: 
        - joint_front_right_prop
        - joint_front_left_prop
        - joint_back_left_prop
        - joint_back_right_prop
    pid: {p: 10000, i: 1, d: 1000}

Can someone please help me out?

Thank you.