Complex sentence: His inheritance was claimed by both his half brother John de Montfort and his niece Joanna of Dreux whose husband Charles of Blois was the nephew of King Philip VI of France.
Split into simpler sentences: His inheritance was claimed by two members of the breton House of Dreux, his half brother John de Montfort and his niece Joan. Joan's husband, Charles of Blois, was the nephew of King Philip VI of France.