Rules for using Hispanic surnames? Reglas para los apellidos hispanos.

Gilbert Paez here. First of all, thank you for letting me part this group. I am working my way through the various areas of the website. It is Great!
My question: Could someone help me with the rules for the proper use of hispanic surnames? Example: My grandmother's maiden name was Romero and my grandfather's last name was Paez. Would my father be Paez Romero?

Cuales son las reglas para el uso de los appellidos en la cultura hispana? Ejemplo: El apellido de mi abuelo era Romero antes de casarse. El apellido de mi abuelo era Paez. El apellido de mi padre fuera Paez Romero o Romero Paez?

Gracias,

Thanks in advance for your help.