Reddit reviews The Glories of Mary

These are the classic books on Mary and on the Rosary. Their fairly cheap too. Don't know about getting them in Portuguese but they are very popular, I assume if you look around you will find a translation.

• The Secret of the Rosary by Saint Louis de Montfort
  
  
• True Devotion to Mary: With Preparation for Total Consecration by Saint Louis de Montfort
  
  
• The Glories of Mary by Saint Alphonsus de Liguori

Another answer - give him a copy of The Glories of Mary and tell him it's an exposé and he should read the whole thing.