His sons had the same last name, they just weren't famous.
Thorhild
People in the medieval times did not have a first and last name. That came as population grew. So Erik was the Erik with red hair and everyone in the area knew which person that was.
Eric the Red's full name was Erik Thorvaldsson. He was also known as Erik the Red due to his red hair and beard. He was a Norse explorer and the founder of the first Norse settlement in Greenland.
born Erik Weisz
The Phantoms first name is Erik, I have never heard his last name but I do not think it is known.
Erik Bartik's birth name is Erik Alexander Bartik.
Erik Loysen's birth name is Erik Loysen.
Erik Silvester's birth name is Erik Herschmann.
Erik Truxa's birth name is Erik Bang.
Erik Taylor's birth name is Erik Taylor.
The Phantom of the Opera (or Erik) doesn't had a last name that is known to the audience. Madame Giry and no other characters make reference to it.
Erik Bye's birth name is Erik Erikssn Bye.