Complex sentence: Gonzalo Fernández de Oviedo indicated that they possessed books of deerskin, where in red and black ink they recorded their deaths and inheritances, so that when there were conflicts or disputes, they could be settled with the opinion of the elders.
Split into simpler sentences: Gonzalo Fernández de Oviedo indicated that they possessed books of deerskin, where in red and black ink they recorded their deaths and inheritances. So, when there were conflicts or disputes, they could be settled with the opinion of the elders.