Can someone help me with an ancestory.com question?

Since, in Mexico, the surname of the Mother, is the one carried by her off-spring, it seems that your Grandparents were likely First cousins and that their mothers may well have been sisters. That might be a help. You need to find out Where they lived, then contact the Parish Priest, to inquire about Baptismal Records. The Catholic Church is very particular about keeping this kind of record and they go back hundreds of years. It's entirely possible that you 'could' trace your family back to Europe, just from these records.