Для правильного вопроса надо знать половину ответа
SELECT `id`
FROM `peoples`
WHERE `id` NOT IN (
SELECT `peoples_id`
FROM `cars`
WHERE `desc` IN ('Mercedes', 'BMW')
)
или
SELECT `p`.`id`
FROM `peoples` AS `p`
LEFT JOIN `cars` AS `c`
ON `c`.`peoples_id` = `p`.`id`
AND `c`.`desc` IN ('Mercedes', 'BMW')
WHERE `c`.`peoples_id` IS NULL