Running tests in modules in parallel testNG surefire

I have created a project that contains multiple modules. In my parent pom.xml I added a surefire plugin.

            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-surefire-plugin</artifactId>
                <version>3.0.0-M7</version>
                <configuration>
                    <suiteXmlFiles>
                        <suiteXmlFile>MyTestSuite.xml</suiteXmlFile>
                    </suiteXmlFiles>
                    <threadCountSuites>16</threadCountSuites>
                    <threadCountClasses>8</threadCountClasses>
                    <threadCountMethods>8</threadCountMethods>
                </configuration>
            </plugin>

Each module contains its own testngsuite.xml file that looks like this:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE suite SYSTEM "https://testng.org/testng-1.0.dtd">
<suite name="Suite">
    <test name="ModuleATests">
        <classes>
            <class name="com.home.Test1"/>
            <class name="com.home.Test2"/>
            <class name="com.home.Test3"/>
        </classes>
    </test>
    <listeners>
        <listener class-name="com.home.MyListener"/>
    </listeners>
</suite>

I would like to execute modules A,B and C in parallel (so all tests in module A have to run sequentially but in parallel with tests from modules B and C). How to achieve it? I have tried many ways but they keep running module after module.

For example, as you can see, I've created an additional file called MyTestSuite.xml (on the same level that I have the parent pom.xml file) to achieve a suite of suites approach:

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE suite SYSTEM "http://testng.org/testng-1.0.dtd">

<suite name="My Custom suite" parallel="classes">
    <suite-files>
        <suite-file path="modules/A/testngsuite.xml"/>
        <suite-file path="modules/B/testngsuite.xml"/>
        <suite-file path="modules/C/testngsuite.xml"/>
    </suite-files>
</suite>

and when running mvn clean test I have an error saying that maven tries to find MyTestSuite.xml in modules A, B and C: modules/A/MyTestSuite.xml is not a valid file