Can I launch multiple instances of the same node in a launch file?

edit

Here is an example of it being done with two nodes of the type ekf_localization_node:

https://github.com/cra-ros-pkg/robot_...

<launch>

  <rosparam command="load" file="$(find robot_localization)/params/dual_ekf_navsat_example.yaml" />

  <node pkg="robot_localization" type="ekf_localization_node" name="ekf_se_odom" clear_params="true"/>

  <node pkg="robot_localization" type="ekf_localization_node" name="ekf_se_map" clear_params="true">
    <remap from="odometry/filtered" to="odometry/filtered_map"/>
  </node>

  <node pkg="robot_localization" type="navsat_transform_node" name="navsat_transform" clear_params="true">
    <remap from="odometry/filtered" to="odometry/filtered_map"/>
  </node>

</launch>

Put different names on each node as seen in the example above.

What type of node are you trying to launch? Might be other conflicts.