How to create overlapping category and bubble maps with CartoCSS

query.sql

SELECT 
	*,
	7 as italians,
	3 as french,
	19 as spanish
FROM 
	populated_places
WHERE 
	name ILIKE 'Barcelona'
UNION ALL
SELECT 
	*,
	10 as italians,
	12 as french,
	4 as spanish
FROM 
	populated_places
WHERE 
	name ILIKE 'Tarragona'
UNION ALL
SELECT 
	*,
	5 as italians,
	7 as french,
	14 as spanish
FROM 
	populated_places
WHERE 
	name ILIKE 'Madrid'
    UNION ALL
SELECT 
	*,
	15 as italians,
	2 as french,
	1 as spanish
FROM 
	populated_places
WHERE 
	name ILIKE 'Zaragoza'

style.css

#layer {
  line-width: 0.1;
  marker-allow-overlap: true;
}
#layer::italians {
    marker-fill: green;
    marker-allow-overlap: true;
  	marker-opacity: 0.5;

    [ italians <= 19] {
       marker-width: 25.0;
    }
    [ italians <= 14] {
       marker-width: 20.0;
    }
    [ italians <= 9] {
       marker-width: 16.7;
    }
    [ italians <= 4] {
       marker-width: 15.0;
    }
    [ italians <= 1] {
       marker-width: 11.7;
    }
}

#layer::french {
  	marker-fill: blue;
    marker-allow-overlap: true;
  	marker-opacity: 0.5;

    [ french <= 19] {
       marker-width: 25.0;
    }
    [ french <= 14] {
       marker-width: 20.0;
    }
    [ french <= 9] {
       marker-width: 16.7;
    }
    [ french <= 4] {
       marker-width: 15.0;
    }
    [ french <= 1] {
       marker-width: 11.7;
    }
}

#layer::spanish {
  marker-fill: red;
  marker-allow-overlap: true;
  marker-opacity: 0.5;

  [ spanish <= 19] {
     marker-width: 25.0;
  }
  [ spanish <= 14] {
     marker-width: 20.0;
  }
  [ spanish <= 9] {
     marker-width: 16.7;
  }
  [ spanish <= 4] {
     marker-width: 15.0;
  }
  [ spanish <= 1] {
     marker-width: 11.7;
  }

}