It seems like everyone descends from Juan de Santiago y Escobar if they're from Aguascalientes. He had like 45 children. I have a Santiago y Escobar that's listed as an hija de padres no conocidos that I suspect is probably an illegitimate child of his although, most of his children appear legitimate.

About Domingo de Santiago and Petronila Perez, i would like to know who their parents are too. They're the parents of my 9th great grandmother, María de Jesús Santiago who married my 9th great grandfather Miguel González. I think all of them are mestizos but both sides of this family are very difficult to research. i think they fall in the period where there's no IM's. The only thing I know about Domingo de Santiago and Petronila Perez is that they are mentioned in this marriage of Miguel González and María de Jesús Santiago:

En la villa de Aguascalientes, en tres de febrero de mil setecientos y veintinueve años habiendo precedido todo lo dispuesto por el Santo Concilio de Trento, y no haber resultado impedimento alguno, asistí al matrimonio, Yo don Nicolás Fernández de Palos, teniente de cura por el señor doctor don Juan Carlos de Casasola, cura de este partido por su Majestad, que por palabras de presentes celebraron Miguel González, mestizo, vecino de esta villa, hijo legítimo de Blas González y María de Tejada: con María de Jesús, así mismo vecino de esta villa, hija legítima de Domingo de Santiago, y de Petrona Pérez, fueron sus padrinos Antonio Valderrama y Rosa María de Chávez, testigos Antonio Macías y Joseph Martín, y por que conste lo firmo conmigo dicho señor.