Simplify the following text for a Grade 8 native English-speaking person.
Original: Parliament offered the Crown not to James 's eldest son , James Francis Edward ( who would have been the heir-apparent under normal circumstances ) , but to William and Mary as joint Sovereigns .
Simplified: Normally , James 's oldest son , James Francis Edward would have been the heir . However , Parliament offered the crown to William and Mary as joint Sovereigns instead .