Is it possible to visualize two robot models in RViz?

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Yes it is possible. The most important thing to remember is namespaces. Check out Multiple robots simulation and navigation.

Here is an example launch file with 3 turtlebot3 robots in gazebo. You will have to visualize your RViz topics.

<launch>
  <!-- <param name="/use_sim_time" value="true"/> -->
  <arg name="model" default="$(env TURTLEBOT3_MODEL)" doc="model type [burger, waffle, waffle_pi]"/>
  <arg name="first_tb3"  default="tb3_0"/>
  <arg name="second_tb3" default="tb3_1"/>
  <arg name="third_tb3"  default="tb3_2"/>  

  <!-- 3 in the same room: -->
  <arg name="first_tb3_x_pos" default="3.0"/>
  <arg name="first_tb3_y_pos" default="4.0"/>
  <arg name="first_tb3_z_pos" default=" 0.0"/>
  <arg name="first_tb3_yaw"   default=" 0.0"/>

  <arg name="second_tb3_x_pos" default=" 3.0"/>
  <arg name="second_tb3_y_pos" default="1.0"/>
  <arg name="second_tb3_z_pos" default=" 0.0"/>
  <arg name="second_tb3_yaw"   default=" 0.0"/>

  <arg name="third_tb3_x_pos" default=" 3.0"/>
  <arg name="third_tb3_y_pos" default=" 3.0"/>
  <arg name="third_tb3_z_pos" default=" 0.0"/>
  <arg name="third_tb3_yaw"   default=" 0.0"/>


  <include file="$(find gazebo_ros)/launch/empty_world.launch">
    <arg name="world_name" value="$(find turtlebot3_gazebo)/worlds/turtlebot3_house.world"/> 
    <arg name="paused" value="false"/>
    <arg name="use_sim_time" value="true"/>
    <!-- <arg name="gui" value="false"/> -->
    <arg name="gui" value="true"/>
    <arg name="headless" value="false"/>
    <arg name="debug" value="false"/>
  </include>  

  <group ns = "$(arg first_tb3)">
    <param name="robot_description" command="$(find xacro)/xacro $(find turtlebot3_description)/urdf/turtlebot3_$(arg model).urdf.xacro" />

    <node pkg="robot_state_publisher" type="robot_state_publisher" name="robot_state_publisher" output="screen">
      <param name="publish_frequency" type="double" value="50.0" />
      <param name="tf_prefix" value="$(arg first_tb3)" />
    </node>

    <node name="spawn_urdf" pkg="gazebo_ros" type="spawn_model" args="-urdf -model $(arg first_tb3) -x $(arg first_tb3_x_pos) -y $(arg first_tb3_y_pos) -z $(arg first_tb3_z_pos) -Y $(arg first_tb3_yaw) -param robot_description" />
  </group>

  <group ns = "$(arg second_tb3)">
    <param name="robot_description" command="$(find xacro)/xacro $(find turtlebot3_description)/urdf/turtlebot3_$(arg model).urdf.xacro" />

    <node pkg="robot_state_publisher" type="robot_state_publisher" name="robot_state_publisher" output="screen">
      <param name="publish_frequency" type="double" value="50.0" />
      <param name="tf_prefix" value="$(arg second_tb3)" />
    </node>

    <node name="spawn_urdf" pkg="gazebo_ros" type="spawn_model" args="-urdf -model $(arg second_tb3) -x $(arg second_tb3_x_pos) -y $(arg second_tb3_y_pos) -z $(arg second_tb3_z_pos) -Y $(arg second_tb3_yaw) -param robot_description" />
  </group>

  <group ns = "$(arg third_tb3)">
    <param name="robot_description" command="$(find xacro)/xacro $(find turtlebot3_description)/urdf/turtlebot3_$(arg model).urdf.xacro" />

    <node pkg="robot_state_publisher" type="robot_state_publisher" name="robot_state_publisher" output="screen">
      <param name="publish_frequency" type="double" value="50.0" />
      <param name="tf_prefix" value="$(arg third_tb3)" />
    </node>

    <node name="spawn_urdf" pkg="gazebo_ros" type="spawn_model" args="-urdf -model $(arg third_tb3) -x $(arg third_tb3_x_pos) -y $(arg third_tb3_y_pos) -z $(arg third_tb3_z_pos) -Y $(arg third_tb3_yaw) -param robot_description" />
  </group>

</launch>