src/it/projects/multimodule/multimodule-siblingParent/parent/pom.xml

<?xml version="1.0"?><project>
  <parent>
    <groupId>org.apache.maven.plugin.assembly.test</groupId>
    <artifactId>it-project-parent</artifactId>
    <version>1</version>
  </parent>

  <modelVersion>4.0.0</modelVersion>
  
  <groupId>test</groupId>
  <artifactId>parent</artifactId>
  <version>1</version>
  
  <packaging>pom</packaging>
  
  <modules>
    <module>../child1</module>
    <module>../child2</module>
  </modules>

  <build>
    <plugins>
      <plugin>
        <artifactId>maven-assembly-plugin</artifactId>
        <inherited>false</inherited>
        <executions>
          <execution>
            <id>assembly</id>
            <phase>package</phase>
            <goals>
              <goal>single</goal>
            </goals>
            <configuration>
              <descriptors>
                <descriptor>src/assemble/src.xml</descriptor>
              </descriptors>
            </configuration>
          </execution>
        </executions>
      </plugin>
    </plugins>
  </build>
</project>