Due to a fire that burned through Santiago during the Dominican Restoration War in 1863, all records in in the city prior to this point were destroyed. Finding information on births, deaths, and marriages, before this point has been made incredibly difficult with this loss, but there are still some ways to piece together the past. The article on consanguinity explains the purpose of marital dispensations. In short when related couples desired to marry, they were required to petition the church for a dispensation. Here is the information for some recovered from Santo Domingo and Puerto Rico.