Complex sentence: However, it was returned to the previous Tonnerre family by the Treaty of Arras but the last male member of that family had died in the meantime and it passed to a sister of the last count by his marriage with Olivier de Husson.
Split into simpler sentences: However, it was returned to the previous Tonnerre family by the Treaty of Arras but the last male member of that family had died in the meantime and it passed. Meanwhile the last masculine member of the family had died however, was left to a sister of the last count by his marriage with Olivier de Husson.