Jose Vitorino Dos Santos Family

My great-grandfather Jose Vitorino Dos Santos (no date of birht) married (no marriage date)Maria Josefa do Coracao de Jesus born abt 1855 in Norte Grande, Sao Jorge, Azores Islands. They had 8 children 5 boys and 3 girls. Three of the sons, Silveria (my grandfather), Jose, and Antonio changed their last name to Pacheco and two, Manuel, Joao kept the Santos name.The girls,Marianna, Isabel, Maria kept their Santos name until married. If anyone knows why the name change or any other information would be greatly appreciated