Complex sentence: They married in 2000 and separated eight years later, after having six sons, the eldest of whom, Nevada Alexander, died of SIDS when he was 10 weeks old.
Split into simpler sentences: They married in 2000 and separated eight years later, after having six sons, the eldest of whom whom died in infancy. Their first child was a boy, Nevada Alexander, who died of SIDS when he was 10 weeks old.