Struggling with the Spanish Naming Rules

With roots in the Middle Ages, Spanish surnames have been around since the 12th century. Children are commonly given two surnames, one from each parent. The middle name (1st surname) is the father's name (apellido paterno), and the last name (2nd surname) is the mother's maiden name (apellido materno).

Trying to keep this naming rule in mind as I set forth on this massive genealogy project to line up the Silvan, Martin, Gonzales, Dovales, Alejo, Hernandez names in the northern part of Spain and the Ruiz, Romero, Garcia and Fernandez names in the southern part of Spain, my brain still pauses and stumbles at times and I have to grab a pencil to draw out the naming map.  Also, deciphering the correct spellings!

Martin is often Martinez.  Silvan is often Silban.  Dovales I thought was Dosales.  All in all, I believe the names are finally correct; now to place them in the proper order.  In Spain, since the father's name is the first surname, or the 'middle' name as we recognize it in America, this means SILVAN is my abuelita's father's name and RUIZ is my abuelo's father's name.
Those are the easy ones since the generation was close enough to personally know on my own.

Then, the generation before them is where the names get fuzzy. 
Abuelita Manuela's father was Juan SILVAN Hernandez.  Her mother was Eustoquia Rita TRASCASAS Marzo.  Why did they give their children Marzo as the middle name for the boys and Trascasas as the middle name for the girls?  Then, there was the exception:  their youngest son (Celestino) had the middle name of Fernandez.  Nobody has the answer to why, why.... cuando???

When abuelita married Bernardo RUIZ Romero, they gave their children the SILVAN name as the middle name for some of their children since it was what Americans call her maiden name, no middle name for others, and American names for others.  I found this happened for several reasons. 

When the Spaniards arrived in California, their Spanish names seemed to broadcast 'poor white trash' in the caste system, as Steve A. put it so eloquently.  Who would want to be called "Spik"?  My father was and so many other Spaniards... so what to do?  They changed their names to sound more American.  (When Spaniards were asked a question upon arrival, they answered with "I no spik-a English" with an intense Spanish accent.   As in many cultures, the new kids on the block were picked on, so the nickname, "Spik" stuck like glue.  Italians were "whops".  Japanese were "Japs".  Chinese were "chinks".  Germans were "krauts".  Demeaning and sad, they wanted to be American!!!

Feliza/Felisa became Alice
Cristencia became Christina
Jose became Joe
Agustin/Augustin became August
Eustoquia Rita became Rita
Francisco became Frank
Maria became Mary or Marie
Miguel became Michael
THEN there were the last names; Martinez was shortened to Martin.  Jorge was changed to George. Souza Bento was shortened to Souza and there's some whisper than some people in that family line used the name "Castro".  Nobody knows who, where or why.

I want my book about the Silvan and Ruiz families to be accurate so rest assured I will nail down the proper name sequence in the Spanish form and how it changed to the American form in my final publication.  For now, the names flit around in my head like a hummingbird around red flowers.