In order to appears in form as Multiline field, system property need to be explicitly set to false.

$this->containsMany('Addresses', [Address::class, 'system' => false]);

I think it would be best to set this property to false by default.

This bring another problem where setting this to false will show up field in Grid/Crud/Table
There should be a way to hide this field in Table but still having them display as Multiline Form field in form.