list($firstname, $surname) = explode(' ', preg_replace("/\([^)]+\)/","",$data['ExistingMemberName' . $value]), 2);
$member = Member::get()->filter(array('FirstName' => '$firstname', 'Surname' => '$surname'))->First();


Error:
Uncaught InvalidArgumentException: ManyManyList::add() expecting a Member object, or ID value