Error mgs during multi vehicle simulation with launch file

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I followed the instruction as mentioned here. when I run

roslaunch px4 multi_uav_mavros_sitl.launch

works fine for default programme but when I added code for one more drone (UAV1 iris_3) and run

roslaunch px4 multi_uav_mavros_sitl.launch

I get following error message although I can see UAVs in Gazebo simulator.

[multi_uav_mavros_sitl.launch] is neither a launch file in package [px4] nor is [px4] a launch file name

The traceback for the exception was written to the log file

I am adding launch file doe here is my launch file:-

<launch>

    <!-- MAVROS posix SITL environment launch script -->

    <arg name="debug" default="false"/>
    <arg name="verbose" default="false"/>
    <arg name="paused" default="false"/>

    <arg name="est" default="ekf2"/>
    <arg name="vehicle" default="iris"/>
    <arg name="world" default="$(find mavlink_sitl_gazebo)/worlds/empty.world"/>

    <arg name="headless" default="false"/>
    <arg name="gui" default="true"/>
    <arg name="ns" default="/"/>

    <arg name="pluginlists_yaml" default="$(find mavros)/launch/px4_pluginlists.yaml" />
    <arg name="config_yaml" default="$(find mavros)/launch/px4_config.yaml" />

    <!-- Load world -->
    <include file="$(find gazebo_ros)/launch/empty_world.launch">
        <arg name="headless" value="$(arg headless)"/>
        <arg name="gui" value="$(arg gui)"/>
        <arg name="world_name" value="$(arg world)" />
        <arg name="debug" value="$(arg debug)" />
        <arg name="verbose" value="$(arg verbose)" />
        <arg name="paused" value="$(arg paused)" />
    </include>

    <!-- UAV1 iris_1-->
    <group ns="uav1">
        <arg name="fcu_url" default="udp://:14540@localhost:14557"/>
        <arg name="gcs_url" value=""/>
        <arg name="tgt_system" value="1"/> 
        <arg name="tgt_component" value="1"/>
        <arg name="rcS1" default="$(find px4)/posix-configs/SITL/init/$(arg est)/$(arg vehicle)_1"/>
        <arg name="ID" value="1"/>

        <include file="$(find px4)/launch/single_vehcile_spawn.launch">
            <arg name="x" value="0"/>
            <arg name="y" value="0"/>
            <arg name="z" value="0"/>
            <arg name="R" value="0"/>
            <arg name="P" value="0"/>
            <arg name="Y" value="0"/>
            <arg name="vehicle" value="$(arg vehicle)"/>
            <arg name="rcS" value="$(arg rcS1)"/>
            <arg name="mavlink_udp_port" value="14560"/>
            <arg name="ID" value="$(arg ID)"/>
        </include>

        <include file="$(find mavros)/launch/node.launch">
            <arg name="pluginlists_yaml" value="$(arg pluginlists_yaml)" />
            <arg name="config_yaml" value="$(arg config_yaml)" />

            <arg name="fcu_url" value="$(arg fcu_url)" />
            <arg name="gcs_url" value="$(arg gcs_url)" />
            <arg name="tgt_system" value="$(arg tgt_system)" />
            <arg name="tgt_component" value="$(arg tgt_component)" />
        </include>
    </group>

    <!-- UAV2 iris_2 -->
    <group ns="uav2">
        <arg name="fcu_url" default="udp://:14541@localhost:14559"/>
        <arg name="gcs_url" value=""/>
        <arg name="tgt_system" value="2"/> 
        <arg name="tgt_component" value="1"/>
        <arg name="rcS2" default="$(find px4)/posix-configs/SITL/init/$(arg est)/$(arg vehicle)_2"/>
        <arg name="ID" value="2"/>

        <include file="$(find px4)/launch/single_vehcile_spawn.launch">
            <arg name="x" value="1"/>
            <arg name="y" value="0"/>
            <arg name="z" value="0"/>
            <arg name="R" value="0"/>
            <arg name="P" value="0"/>
            <arg name="Y" value="0"/>
            <arg name="vehicle" value="$(arg vehicle)"/>
            <arg name="rcS" value="$(arg rcS2)"/>
            <arg name="mavlink_udp_port" value="14562"/>
            <arg name="ID" value="$(arg ID)"/>
        </include>

        <include file="$(find mavros)/launch/node.launch">
            <arg name="pluginlists_yaml" value="$(arg pluginlists_yaml)" />
            <arg name="config_yaml" value="$(arg config_yaml)" />

            <arg name="fcu_url" value="$(arg fcu_url)" />
            <arg name="gcs_url" value="$(arg gcs_url)" />
            <arg name="tgt_system ...