I'm also a descendant of Juan Pantaleon and Gertrudis Vela through their daughter Antonia (Antonia is a sister to the Luisa in your family.
I recently found a great source that should answer a lot of questions for you...because these ancestors of yours and mine were given land by the Spanish government in what is now South Texas. Here's the book title and information:
Joel Rene Escobar ed., "Family Tree Book: The Seabury Papers by Francis William Seabury," New Santander Press, Edinburg TX, 31 July 1995.
In it you will find the family trees of
-Juan Pantaleon Yzaguirre -Lazaro Vela (father of Gertrudis Vela) -Joaquin Garcia (father of Jose Maria Garcia, husband of Luisa) -Jose Manuel de la Garza Montemayor (husband of Maria Desideria Garcia)