Complex sentence: Joseph and John Phillips owners a farm of 116 acres, in Monmouthshire unbeknowns to them their neighbours the Tredegar Iron Company, had extracted 2000 tons of coal from under their farm.
Split into simpler sentences: Joseph and John Phillips owned a farm of 116 acres, in Monmouthshire. Unbeknownst to them their neighbours, the Tredegar Iron Company, extracted 2000 tons of coal from under their farm.