Complex sentence: Lockhart's uncle was John Gibson Lockhart, eminent writer, poet and biographer of Sir Walter Scott, his mother Louisa Blair was a daughter of Janet Muir; sister of the Scottish political reformer Thomas Muir of Huntershill.
Split into simpler sentences: Lockhart's uncle was John Gibson Lockhart, eminent writer, poet and biographer of Sir Walter Scott. His mother Louisa Blair was a daughter of Janet Muir and sister of the Scottish political reformer Thomas Muir of Huntershill.