double surnames

["Erlinda Castanon-Long" <longsjourney@...>]

I'm hoping you can help me with double surnames.  Is there a 
difference when they use De or Y? Such as Alvares del Castillo or 
Ochoa y Garibay?  How long did they usually keep the double surname?  
I haven't found a reason why some families ended up using the surname 
they chose.. Villasenor y Jaso, some went Villasenor and others went 
Jaso.. same family!

I have gone from records in Tamazula Jalisco to Chilchota Michoacan.  
So many families from that part of Jalisco came from this area of 
Michoacan in the later 1700's.  In doing marriage records from there 
I'm finding it not unusual to have the actual marriage in the home of 
a family member, was that normal for the mid 1750's?
Linda in Everett