I am a direct descendant of Antonio de Tafoya Altamirano, Cristobal's brother. Our lineage is posted on the Great New Mexico Data Base which is found on the Hispanic Genealogy Research Center of New Mexico's web site, hgrc-nm.org. We know, of course, about Cristobal and Juan but have never been able to go back further than Juan de Tafoya Altamirano's birth date. We do not know who his parent's were. Is is possible that you may have had better luck?