Complex sentence: Nieto claimed to have been asleep during the attack and dreaming that he was defending himself against aggressive ostriches, but his children declared that he had recognized them and told his son to not turn on the lights because their mother (gravely injured already) was sleeping.
Split into simpler sentences: Nieto claimed to have been asleep during the attack and dreaming that he was defending himself against aggressive ostriches. However, his children stated that he had recognized them and had even told his son to not turn on the lights because their mother (gravely injured already) was sleeping.